Controlled vapor deposition of biocompatible coatings over surface-treated substrates

ABSTRACT

We have developed an improved vapor-phase deposition method and apparatus for the application of layers and coatings on various substrates. The method and apparatus are useful in the fabrication of biofunctional devices, Bio-MEMS devices, and in the fabrication of microfluidic devices for biological applications. In one important embodiment, a siloxane substrate surface is treated using a combination of ozone and UV radiation to render the siloxane surface more hydrophilic, and subsequently a functional coating is applied in-situ over the treated surface of the siloxane substrate.

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/123,487, filed May 5, 2005 and entitled “Controlled VaporDeposition Of Biocompatible Coatings For Medical Devices”, which iscurrently pending. This application is also a continuation-in-part ofU.S. patent application Ser. No. 11/112,664, filed Apr. 21, 2005, andentitled “Controlled Vapor Deposition of Multilayered Coatings AdheredBy An Oxide Layer”, which is a continuation in part of U.S. patentapplication Ser. No. 10/996,520, filed Nov. 23, 2004, and entitled“Controlled Vapor Deposition of Multilayered Coatings Adhered by anOxide Layer”, which is a continuation in part of U.S. patent applicationSer. No. 10/862,047, filed Jun. 4, 2004, and entitled “ControlledDeposition of Silicon-Containing Coatings Adhered by an Oxide Layer”,all of which applications are currently pending. This application isalso a continuation-in-part of U.S. patent application Ser. No.11/048,513, filed Jan. 31, 2005, and entitled “High Aspect RatioPerformance Coatings for Biological Microfluidics”, which is also acontinuation in part of U.S. patent application Ser. No. 10/862,047which is recited above. Priority is claimed under all five of the priorpending applications, each of which has more than one inventor in commonwith the present application. All five of these prior pending U.S.patent applications are hereby incorporated by reference in theirentireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to the treatment of substrate surfaces toimprove the long term performance of biocompatible coatings which areapplied over the substrate surface. The invention also pertains to thesurface treatment of implants and devices used in medical applicationswhich require hydrophilic, biocompatible interfaces with bodily tissuesand fluids.

2. Brief Description of the Background Art

While a portion of the Background Art disclosed herein is prior art, thepresence of any disclosure in this Background Art is not to be construedas an admission that the disclosure is prior art.

In the biological field, the surface characteristics of a substratecontrol the functioning of that substrate relative to fluids with whichthe substrate surface comes in contact. Since known living organismsrely heavily on the presence of water, the hydrophilicity orhydrophobicity of a given surface plays a major role in determiningwhether a medical device can perform well in the environment in which itis to function. The surface of the medical device must be designed toprovide biocompatibility with fluids it is to contact in theenvironment, and may be designed to achieve a particular interactionwith the fluids it contacts. The ability of a medical device to functioneither in-vivo or in-vitro depends on the surface presented by themedical device. For example, with respect to an implant which is used inmedical applications, the ability of the implant to integrate into thelocation at which it is placed and to function in combination withsurrounding tissues and fluids depends significantly on thehydrophilicity or hydrophobicity of the implant surface, and frequentlydepends on the presence or absence on the surface of the implant ofchemical compounds having particular properties. With respect to amedical device surface used for chemical analysis, for example, thedevice must provide a functional surface which enables the particularanalytical function. We previously described a number of biocompatiblecoatings which could be applied over various substrates to provide abiocompatible surface. Since our initial work, we have been working toimprove the lifetime of the biocompatibility of the coatings underambient conditions.

The need for biocompatible films and, in particular, for hydrophilic,neutral biocompatible surfaces that resist adhesion and growth ofprotein, lipids, and bacteria, drives the search for new materialscompatible with medical and biological applications. For example, thoseskilled in the art have long recognized the need for rendering thesurface of contact lenses hydrophilic in order to improve theirbiocompatibility or wettability by tear fluid in the eye. This isnecessary to improve the wear comfort of contact lenses and/or to extendtheir resistance to bacterial infection, inflammation, and other adverseeffects resulting from incompatibility of the lens with the human bodyand its functions.

In the case of contact lenses, in particular, the lens surface must beresistant to bacterial growth and infection, and must also behydrophilic to allow for efficient binding of water by the lens andsufficient flow of oxygen to the surface of the eye.Carbohydrate-comprising coatings are of particular interest, as theyresemble the natural coating of a human cell and are less prone toinflammation and irritation of tissue due to chemical and biologicalincompatibility. They also have a lubricating effect caused by theirhigh surface energy, are optically clear, and facilitate exchange offluids between the surface of the coated device and the body.

In many applications where the wear on the coating is likely to occurdue to mechanical contact or where fluid flow is to occur over thesubstrate surface on which the layer of coating is present, it ishelpful to have the coating chemically bonded directly to the substratesurface via chemical reaction of active species which are present in thecoating reactants/materials with active species on the underlyingsubstrate surface. In addition, particular precursor materials may beselected which are known to provide particular functional moieties.

With respect to layers and coatings which are chemically bonded to amedical device surface, there are a number of areas of particularcurrent interest. By way of example, and not by way of limitation,surface structure and exterior coatings on that surface structure may beused for biotechnology applications where the surface wetting propertiesand functionality are useful for analytical purposes, for controllingfluid flow and sorting of fluid components, and for altering thecomposition of components which come into contact with the surface, forexample.

Due to the nanometer size scale of some of medical device applicationswhich employ coatings exhibiting specialized functionality, a need hasgrown for improved methods of controlling the formation of the coating,including the formation of individual layers within a multi-layeredcoating, for example. Typically such coatings range in thickness fromabout 1 nm (10 Å) to about 1 micron (μ). At the present time,approximately 95% of the new applications for medical device coatingsmake use of a coating thickness which is less than 100 nm, with a numberof applications requiring a coating thickness in the range of about 50nm to 100 nm. Historically, surface coatings for medical devices havebeen applied by contacting a device substrate surface with a liquidcoating material. While this technique enables efficient coatingdeposition, it frequently results in limited control over the surfaceproperties of the applied coating. In the case of coating a surface of amedical device which must function on a nanometer scale, use of liquidphase processing limits device yield due to contamination and capillaryforces. More recently, deposition of coatings from a vapor-phase hasbeen used in an attempt to improve coating properties. However, thecommon vapor-phase deposition methods may not permit sufficient controlof the molecular level reactions taking place during the deposition ofsurface bonding layers or during the deposition of functional coatings,when the deposited coating needs to exhibit functional surfaceproperties on a nanometer (nm) scale.

For purposes of illustrating methods of coating formation where vaporousand liquid precursors are used to deposit a coating on a substrate,applicants would like to mention the following publications and patentswhich relate to methods of coating formation, for purposes ofillustration. Most of the background information provided is withrespect to various chlorosilane-based precursors; however it is notintended that the present invention be limited to this class ofprecursor materials. In addition, applicants would like to make it clearthat some of this Background Art is not prior art to the presentinvention. It is mentioned here because it is of interest to the generalsubject matter.

In an article by Barry Arkles entitled “Tailoring surfaces withsilanes”, published in CHEMTECH, in December of 1977, pages 766-777, theauthor describes the use of organo silanes to form coatings which impartdesired functional characteristics to an underlying oxide-containingsurface. In particular, the organo silane is represented asR_(n)SiX_((4-n)) where X is a hydrolyzable group, typically halogen,alkoxy, acyloxy, or amine. Following hydrolysis, a reactive silanolgroup is said to be formed which can condense with other silanol groups,for example, those on the surface of siliceous fillers, to form siloxanelinkages. Stable condensation products are said to be formed with otheroxides in addition to silicon oxide, such as oxides of aluminum,zirconium, tin, titanium, and nickel. The R group is said to be anonhydrolyzable organic radical that may possess functionality thatimparts desired characteristics. The article also discusses reactivetetra-substituted silanes which can be fully substituted by hydrolyzablegroups and how the silicic acid which is formed from such substitutedsilanes readily forms polymers such as silica gel, quartz, or silicatesby condensation of the silanol groups or reaction of silicate ions.Tetrachlorosilane is mentioned as being of commercial importance sinceit can be hydrolyzed in the vapor phase to form amorphous fumed silica.

The article by Dr. Arkles shows how a substrate with hydroxyl groups onits surface can be reacted with a condensation product of anorganosilane to provide chemical bonding to the substrate surface. Thereactions are generally discussed and, with the exception of theformation of amorphous fumed silica, the reactions are between a liquidprecursor and a substrate having hydroxyl groups on its surface. Anumber of different applications and potential applications arediscussed.

In an article entitled “Organized Monolayers by Adsorption. 1. Formationand Structure of Oleophobic Mixed Monolayers on Solid Surfaces”,published in the Journal of the American Chemical Society, Jan. 2, 1980,pp. 92-98, Jacob Sagiv discussed the possibility of producing oleophobicmonolayers containing more than one component (mixed monolayers). Thearticle is said to show that homogeneous mixed monolayers containingcomponents which are very different in their properties and molecularshape may be easily formed on various solid polar substrates byadsorption from organic solutions. Irreversible adsorption is said to beachieved through covalent bonding of active silane molecules to thesurface of the substrate.

U.S. Pat. No. 5,002,794 to Ratner et al., issued Mar. 26, 1991,describes a method of controlling the chemical structure of polymericfilms formed by plasma deposition. An important aspect of the methodinvolves controlling the temperature of the substrate and the reactor tocreate a temperature differential between the substrate and reactor suchthat the precursor molecules are preferentially adsorbed or condensedonto the substrate either during plasma deposition or between plasmadeposition steps. (Abstract) This reference discusses the immobilizationof poly(ethylene glycol), also referred to as PEG or as polyethyleneoxide (PEO). The application of PEG-like thin films, grafted onto a widevariety of substrates, is described as carried out using a plasmadeposition apparatus. Substrates are said to be cleaned by etching withan argon plasma in some instances. An object to be treated is placed ina vacuum chamber, and reactant precursor is introduced into the chamberat a specified rate so as to maintain a constant pressure in thereactor. A power supply is used to maintain a plasma at a set powerlevel during the deposition. The disclosure teaches that, depending onthe length of time the plasma is maintained, the thickness of thedeposited films may be controlled as desired. The precursor material isintroduced into the reaction vessel and pressure and flow of theprecursor material are stabilized, with the plasma deposition andcondensation carried out simultaneously or alternately for any desiredlength of time. After the deposition is complete, the coated specimensmay be permitted to remain in the presence of the precursor “to permitthe chemical reactions in the film to go to completion”. This isreferred to as a quench step. The disclosure of this reference is herebyincorporated by reference in its entirety.

Kevin L. Prime et al. published an article entitled “Self-AssembledOrganic Monolayers: Model Systems for Studying Adsorption of Proteins atSurfaces” in Science 1991, 252, pp. 1164-1167. Self-assembled monolayers(SAMs) of ω-functionalized long-chain alkanethiolates on gold films aredescribed as excellent model systems with which to study theinteractions of proteins with organic surfaces. Monolayers containingmixtures of hydrophobic (methyl terminated) and hydrophilic [hydroxyl-,maltose-, and hexa(ethylene glycol)-terminated] alkanethiols are said tobe tailored to select specific degrees of adsorption. The SAMS wereprepared by the chemisorption of alkanethiols from 0.25 mM solutions inethanol or methanol onto thin (200±20 nm) gold films supported onsilicon wafers. The hexa(ethylene glycol)-terminated SAMS are said to bethe most effective in resisting protein adsorption. (Abstract) Thesubject matter of this article is hereby incorporated by reference inits entirety.

In June of 1991, D. J. Ehrlich and J. Melngailis published an articleentitled “Fast room-temperature growth of SiO₂ films by molecular-layerdosing” in Applied Physics Letters 58 (23), pp. 2675-2677. The authorsdescribe a dosing technique for room-temperature growth of α-SiO₂ thinfilms, which growth is based on the reaction of H₂O and SiCl₄adsorbates. The reaction is catalyzed by the hydrated SiO₂ growthsurface, and requires a specific surface phase of hydrogen-bonded water.Thicknesses of the films is said to be controlled to molecular-layerprecision; alternatively, fast conformal growth to rates exceeding 100nm/min is said to be achieved by slight depression of the substratetemperature below room temperature. Potential applications such astrench filling for integrated circuits and hermetic ultrathin layers formultilayer photoresists are mentioned. Excimer-laser-induced surfacemodification is said to permit projection-patterned selective-areagrowth on silicon.

An article entitled “Atomic Layer Growth of SiO₂ on Si(100) Using TheSequential Deposition of SiCl₄ and H₂O” by Sneh et al. in Mat. Res. Soc.Symp. Proc. Vol 334, 1994, pp. 25-30, describes a study in which SiO₂thin films were said to be deposited on Si(100) with atomic layercontrol at 600° K (≅327° C.) and at pressures in the range of 1 to 50Torr using chemical vapor deposition (CVD).

A. A. Campbell et al. presented a paper “Low Temperature SolutionDeposition of Calcium Phosphate Coatings For Orthopedic Implants” at theAmerican Ceramic Society Meeting, Apr. 24-28, 1994, in Indianapolis,Ind., published by NTiS, document DE94014497, which describes the growthof calcium phosphate coatings from aqueous solution onto a derivatizedself-assembled monolayer (SAM) which was covalently bound to a titaniummetal substrate. The SAM molecules were reported as providing an [ideal]connection between the metal surface and the calcium phosphate coating.A trichlorosilane terminus of the SAM molecule was reported as insuringcovalent attachment to the substrate, while a functionalized “tail” ofthe SAM molecule induced heterogeneous nucleation of the calciumphosphate coating from supersaturated solutions. (Abstract) Theintroduction of the article explains that bone and dental implanttechnology is currently inadequate. The bond between bone and implantmaterials (such as Ti and metal alloys) is said to fail, requiringadditional surgery to remove and replace the implant after only a fewyears of use. To date, hydroxyapatite (HAP) coatings are said to haveshown exceptional promise as bioactive coatings for metallic implantdevices. It is commented that the apatite may be able to partiallydissolve, intergrow, and become partially incorporated with the apatitein growing bone, forming a coating: bone interface as strong as the boneitself. The subject matter of this reference is hereby incorporated byreference in its entirety.

U.S. Pat. No. 5,328,768 to Goodwin, issued Jul. 12, 1994, discloses amethod and article wherein a glass substrate is provided with a moredurable non-wetting surface by treatment with a perfluoroalkyl alkylsilane and a fluorinated olefin telomer on a surface which comprises asilica primer layer. The silica primer layer is said to be preferablypyrolytically deposited, magnetron sputtered, or applied by a sol-gelcondensation reaction (i.e. from alkyl silicates or chlorosilanes). Aperfluoroalkyl alkyl silane combined with a fluorinated olefin telomeris said to produce a preferred surface treatment composition. Thesilane/olefin composition is employed as a solution, preferably in afluorinated solvent. The solution is applied to a substrate surface byany conventional technique such as dipping, flowing, wiping, orspraying.

In U.S. Pat. No. 5,372,851, issued to Ogawa et al. on Dec. 13, 1995, amethod of manufacturing a chemically adsorbed film is described. Inparticular a chemically adsorbed film is said to be formed on any typeof substrate in a short time by chemically adsorbing a chlorosilanebased surface active-agent in a gas phase on the surface of a substratehaving active hydrogen groups. The basic reaction by which achlorosilane is attached to a surface with hydroxyl groups present onthe surface is basically the same as described in other articlesdiscussed above. In a preferred embodiment, a chlorosilane basedadsorbent or an alkoxyl-silane based adsorbent is used as thesilane-based surface adsorbent, where the silane-based adsorbent has areactive silyl group at one end and a condensation reaction is initiatedin the gas phase atmosphere. A dehydrochlorination reaction or ade-alcohol reaction is carried out as the condensation reaction. Afterthe dehydrochlorination reaction, the unreacted chlorosilane-basedadsorbent on the surface of the substrate is washed with a non-aqueoussolution and then the adsorbed material is reacted with aqueous solutionto form a monomolecular adsorbed film.

Patrick W. Hoffmann et al., in an article published by the AmericanChemical Society, Langmuir 1997, 13, pp. 1877-1880, entitled: “VaporPhase Self-Assembly of Fluorinated Monolayers on Silicon and GermaniumOxide” describe the surface coverage and molecular orientation ofmonomolecular thin organic films on a Ge/Si oxide substrate. A gas phasereactor was said to have been used to provide precise control of surfacehydration and reaction temperatures during the deposition ofmonofunctional perfluorated alkylsilanes. Complete processing conditionsare not provided, and there is no description of the apparatus which wasused to apply the thin films.

Miqin Zhang et al., in an article entitled “Hemocompatible PolyethyleneGlycol Films on silicon”, published in Biomedical Microdevices, 1(1),pp. 81-87 (1998), describe the functionalization of polyethylene glycol(PEG) by SiCl₃ groups on its chain ends, and the reaction of the PEGorganosilicon derivatives with hydroxylated groups on silicon surfaces.The reactant preparations and the attachment of PEG film onto siliconsurfaces were carried out in a glass apparatus which prevented exposureto the atmosphere. Nitrogen was used as the isolation gas, and theprecursor formation reactions were carried out in solutions, withattachment of the precursor to the silicon surface by contact of aprecursor solution with the silicon surface.

In another article entitled “Proteins and cells on PEG immobilizedsilicon surfaces”, published in Biomaterials 19 (1998) pp. 953-960,Zhang et al. describe the modification of silicon surfaces by covalentattachment of self-assembled polyethylene glycol (PEG) film. Adsorptionof albumin, fibrinogen, and IgG to PEG immobilized silicon surfaces wasstudied to evaluate the non-fouling and non-immunogenic properties ofthe surfaces. The adhesion and proliferation of human fibroblast andHela cells onto the modified surfaces were investigated to examine theirtissue biocompatibility. Coated PEG chains were said to show theeffective depression of both plasma protein adsorption and cellattachment to the modified surfaces. The mechanisms accounting for thereduction of protein adsorption and cell adhesion on modified surfaceswere discussed. (Abstract) This article is hereby incorporated byreference in its entirety. PEG was immobilized on silicon by thefunctionalization of a PEG precursor in the manner described in thearticle discussed above.

In an article entitled “Vapor phase deposition of uniform and ultrathinsilanes” by Yuchun Wang et al, SPIE Vol. 3258-0277-786X/98 pp. 20-38,the authors discuss the need for ultrathin coatings on the surfaces ofbiomedical microdevices to regulate hydrophilicity and to minimizeunspecific protein adsorption. It is recommended that silane“monolayers” which are typically formed on surfaces in organic solution,be vapor deposited instead, to reduce the formation of variablethickness films and the formation of submicron aggregates or islands onthe silicon substrate surface. The vapor phase coating method is carriedout at ambient pressure using nitrogen to flush out the system, andsubsequently using nitrogen as a carrier gas for the reactants.(Abstract) It is mentioned that an alternative strategy consists of(applying) coating silanes in high vacuum, but no process conditionswere provided. Biomedical devices formed by the method are said to beuseful in the formation of microfabricated filters which regulatehydrophilicity of a surface and minimize unspecific protein absorption.

Darrel J. Bell et al., in an article entitled “Using poly(ethyleneglycol) silane to prevent protein adsorption in microfabricated siliconchannels”, SPIE Vol. 3258-0277-786X/98, pp. 134-140, describe progresstoward achieving a long-term antifouling surface for use in chemical andbiological agent purification and detection. Poly(ethylene glycol) (PEG)silane is covalently bonded to the hydroxyls of an oxide layer on asilicon device surface and the Pyrex cover slip. (Abstract) Patternedsilicon wafers are thermally oxidized to provide an oxide layer forsilanization chemistry. (Page 135) A PEG-3400 silane was dissolved inanhydrous toluene to form either a 1% or a 2% solution. Silicon andPyrex® samples were placed in stirred PRG solution for varying times(24, 4 and 1.5 hours) to deposit a layer of PEG. Subsequently, allsamples underwent 2-5 minute sonicating rinses in fresh anhydroustoluene before being cured for 14 hours at a temperature of 125° C. in avacuum under 30 in. Hg.

In an article entitled “SiO₂ Chemical Vapor Deposition at RoomTemperature Using SiCl₄ and H₂O with an NH₃ Catalyst”, by J. W. Klausand S. M. George in the Journal of the Electrochemical Society, 147 (7)2658-2664, 2000, the authors describe the deposition of silicon dioxidefilms at room temperature using a catalyzed chemical vapor depositionreaction. The NH₃ (ammonia) catalyst is said to lower the requiredtemperature for SiO₂ CVD from greater than 900° K to about 313-333° K.

U.S. Patent Publication No. US 2002/0065663 A1, published on May 30,2002, and titled “Highly Durable Hydrophobic Coatings And Methods”,describes substrates which have a hydrophobic surface coating comprisedof the reaction products of a chlorosilyl group containing compound andan alkylsilane. The substrate over which the coating is applied ispreferably glass. In one embodiment, a silicon oxide anchor layer orhybrid organo-silicon oxide anchor layer is formed from a humidifiedreaction product of silicon tetrachloride or trichloromethylsilanevapors at atmospheric pressure. Application of the oxide anchor layer isfollowed by the vapor-deposition of a chloroalkylsilane. The siliconoxide anchor layer is said to advantageously have a root mean squaresurface (RMS) roughness of less than about 6.0 nm, preferably less thanabout 5.0 nm and a low haze value of less than about 3.0%. The RMSsurface roughness of the silicon oxide layer is preferably said to begreater than about 4 nm, to improve adhesion. Too small an RMS surfaceis said to result in the surface being too smooth, that is to say aninsufficient increase in the surface area/or insufficient depth of thesurface peaks and valleys on the surface. However, too great an RMSsurface area is said to result in large surface peaks, widely spacedapart, which begins to diminish the desirable surface area forsubsequent reaction with the chloroalkylsilane by vapor deposition.

Simultaneous vapor deposition of silicon tetrachloride anddimethyldichlorosilane onto a glass substrate is said to result in ahydrophobic coating comprised of cross-linked polydimethylsiloxane whichmay then be capped with a fluoroalkylsilane (to provide hydrophobicity).The substrate is said to be glass or a silicon oxide anchor layerdeposited on a surface prior to deposition of the cross-linkedpolydimethylsiloxane. The substrates are cleaned thoroughly and rinsedprior to being placed in the reaction chamber.

U.S. Pat. No. 5,936,703 to Miyazaki et al, issued Aug. 10, 1999describes a specialized alkoxysilane compound or its acid-processedreaction product, which is used as a surface processing solution for acontact lense surface. The compound is said to be capable of providinghydrophilicity to the surface of various substrates which are treatedwith a surface processing solution of the compound. The hydrophilicityis said to be peculiar to the specialized alkoxysilane compound, whereasother silane coupling agents containing alkoxysilane groups are said tohave been used to provide hydrophobic properties to the surface ofinorganic or organic materials. (Abstract and Col. 1, lines 31-38.)

T. M. Mayer et al. describe a “Chemical vapor deposition offluoroalkylsilane monolayer films for adhesion control inmicroelectromechanical systems” in J. Vac. Sci. Technol. B 18(5),September/October 2000. This article mentions the use of a remotelygenerated microwave plasma for cleaning a silicon substrate surfaceprior to film deposition, where the plasma source gas is either watervapor or oxygen.

U.S. Pat. No. 6,200,626 to Grobe, III et al., issued Mar. 13, 2001,describes an optically clear, hydrophilic coating produced on thesurface of a silicone medical device by sequentially subjecting thesurface of a lens to plasma polymerization reaction in a hydrocarbonatmosphere, to produce a carbon layer, then graft polymerizing a mixtureof monomers comprising hydrophilic monomers onto the carbon layer. Theinvention is said to be especially useful for forming a biocompatiblecoating on silicone hydrogen contact lenses. (Abstract) The invention issaid to be directed toward treatment of silicone medical devices. (Col.3, lines 17-19.) Various silicon-containing monomers and a siliconehydrogel material are described, which may be used to provide asubstrate. (Col. 3-Col. 6.)

Typically, the substrate surface is plasma oxidized, using a strongoxidizing plasma (Col. 8, lines 11-19), followed byplasma-polymerization deposition with a C1 to C10 saturated orunsaturated hydrocarbon to form a polymeric carbonaceous primarycoating, followed by a grafting of a mixture of monomers (inclusive ofmacromers) onto the carbonaceous primary coating, to form a hydrophilic,biocompatible secondary coating. (Col. 7, lines 40-49.) The graftingreaction may employ an initiator, or the carbonaceous layer may beactivated to promote the covalent attachment of polymer to the surface.The grafting polymer may be formed by using an aqueous solution of anethylenically unsaturated monomer or a mixture of monomers capable ofundergoing graft addition polymerization. (Col. 9, lines 18-53.)

U.S. Pat. No. 6,213,604 to Valint, Jr. et al., issued Apr. 10, 2001,describes plasma surface treatment of silicone hydrogel contact lenses.In particular, the surface of a contact lens is modified to increase itshydrophilicity by coating the lens with a carbon-containing layer madefrom a diolefinic compound having 4 to 8 carbon atoms. In oneembodiment, an optically clear, hydrophilic coating is provided upon thesurface of a silicone hydrogel lens by sequentially subjecting thesurface of the lens to: a plasma oxidation reaction, followed by aplasma polymerization reaction in the presence of a diolefin, in theabsence of air (in the absence of oxygen or nitrogen, where “absence” isdefined to mean at a concentration of less than 10% by weight of oxygenor nitrogen, preferably less than two percent, and most preferably zeropercent). Finally, the resulting carbon-containing layer is renderedhydrophilic by a further plasma oxidation reaction or by the attachmentof a hydrophilic polymer chain. (Abstract and Col. 2, lines 44-53).Silicone lenses which are hydrogels can absorb and retain water in anequilibrium state. Hydrogels generally have a water content greater thanabout five weight percent and more commonly between about ten to abouteighty weight percent. (Col. 1, lines 19-27.)

D. M. Bubb et al., in an article entitled “Vapor deposition of intactpolyethylene glycol thin films”, published in Appl. Phys. A (2001)Digital Object Identified (DOI) 10.1007/s003390100884, describe thedeposition of polyethylene glycol (PEG) films of average molecularweight, 1400 amu, by both matrix assisted pulsed laser evaporation(MAPLE) and pulsed laser deposition (PLD). Films were deposited on NaClplates, Si(111) wafers, and glass slides. The MAPLE deposited films aresaid to have shown nearly identical resemblance to the startingmaterial, while the PLD films did not. (Abstract) In MAPLE, the materialto be deposited is dissolved in an appropriate solvent, typically at 0.1to 2.0 wt. % concentration and is frozen solid. The composite isevaporated using a pulsed laser. The vaporized solvent is said not toform a film, and is pumped away by the vacuum system in the filmdeposition chamber.

V. A. Shamamian et al., in an article entitled “Mass SpectrometricCharacterization of Pulsed Plasmas for Deposition of Thin PolyethyleneGlycol-Like Polymer Films”, published in 2001 by the Society of VacuumCoaters 505/856-7188, 44th Annual Technical Conference Proceedings,Philadelphia, Apr. 21-26, 2001, describe the characterization of pulsedinductively coupled rf plasmas of two organic precursor molecules,isopropyl alcohol and 1,4 dioxane using Langmuir probes and in situ massspectrometry. The ultimate goal of the work was to develop predictablemodels for PECVD processes for thin polymer films with functionalizedsurfaces. (Abstract) Polyethylene glycol, or PEG-like structures werechosen as the target PECVD functional groups. The precursors mentionedabove are precursors for a cyclic version of a diethylene glycolstructure.

Daniel M. Bubb et al., in an article entitled “Resonant infraredpulsed-laser deposition of polymer films using a free-electron laser”,published in J. Vac. Sci. Technol. A 19(5), September/October 2001, pp.2698-2702, describe the pulsed laser deposition (PLD) of thin films ofpolyethylene glycol (MW 1500) using both a tunable infrared (λ=2.9 μm,3.4 μm) and ultraviolet laser (λ≃193 nm). When the IR laser is tuned toa resonant absorption in the polymer, the IR PLD thin films are said tobe identical to the starting material, where the UV PLD are said to showsignificant structural modification. (Abstract)

U.S. Pat. No. 6,475,808 to Wagner et al., issued Nov. 5, 2002, describesarrays of proteins which are used for in vitro screening of biomolecularactivity. Methods of using the protein arrays are also disclosed. Theprotein arrays are said to be immobilized on one or more organic thinfilms on a substrate surface. (Abstract) A number of different methodsfor immobilizing the proteins are discussed. One of the methodsdescribed is the use of a self-assembled monolayer having an end group Xavailable which provides chemisorption or physisorption of the monolayeronto the surface of a substrate. If the substrate is a material such assilicon, silicon oxide, or a metal oxide, then X may be amonohalosilane, dihalosilane, trihalosilane, trialkoxysilane,dialkoxysilane, or a monoalkoxysilane. (Col. 15, lines 31-51) The otherend group of the self-assembled monolayer, Y, provides coupling with theprotein readily under normal physiological conditions not detrimental tothe activity of the protein. The functional group Y may either form acovalent linkage or a noncovalent linkage with the protein. (Col. 16,lines 33-49.) Particular deposition techniques for application of theself-assembled monolayer are not disclosed.

Ketul C. Popat et al., in an article entitled “Characterization of vapordeposited poly(ethylene glycol) films on silicon surfaces for surfacemodification of microfluidic systems”, in the J. Vac. Sci. Technol. B21(2), March/April 2003 at pages 645-654, discuss microfluidic systemswhich employ Poly (ethylene glycol) (PEG) as a surface coating to reduceprotein adsorption on microfluidic surfaces. The PEG is said to reduceprotein adsorption on the microfluidic surface. The authors developed amethod of vapor deposition for the PEG which is said to be helpful whenthe size of microfluidic surfaces is in the micro/nanoscale range. Filmsdeposited using the vapor deposition technique are said to decreaseprotein adsorption by 80% and to be stable for a period of 4 weeks.(Abstract).

The authors describe the use of silanes as precursors or bridges toconnect a PEG molecule to a surface. The silane precursors are describedas highly sensitive to moisture, forming aggregates and lumps on asilicon surface in the presence of moisture. These aggregates are saidto clog or mask micro/nano-size features on devices. The article focuseson the vapor deposition of silane and, subsequently, PEG on siliconsurfaces in a moisture free nitrogen atmosphere. To deposit PEG on asurface, a basic starting molecule of ethylene oxide is used incombination with a gas catalyst. (Page 646) A substrate surface was asilicon wafer, p-type, boron doped, with (1,0,0) orientation. Thesilicon surface was treated with ammonium hydroxide and hydrogenperoxide in distilled water to attach an —OH group to the surface.Ethylene oxide in vapor phase was used to grow PEG on the siliconsurface. The surface was first silanized with a reactive end groupsilane like 3-APTMS. This is a bifunctional organosilane possessing areactive primary amine and a hydrolyzable inorganic trimethoxysilylgroup. This is a short-chained silane with a boiling point of 194° C. Itis said to violently react with water and to tend to polymerize onsurfaces forming lumps and aggregates. Therefore the application of thesilane to the silicon surface is said to be carried out in a moisturefree environment to reduce the risk of formation of lumps and aggregateson the substrate surface. (Page 647)

Boron trifluoride was used as a gaseous catalyst in combination with theethylene oxide during formation of the PEG on the silicon surface. Theboron trifluoride is said to be a weak Lewis acid which accepts a freepair of electrons of —NH₂ on APTMS, to make a reaction site availablefor a reactive ethylene oxide molecule to attach and then an additionalpolymerization reaction to form PEG on the substrate surface. The PEGcomposition is said to be controlled by the concentration of ethyleneoxide and the polymerization time. The reaction is said to be terminatedby flowing inert gas over the surface after an appropriate time.Nitrogen gas is used at specific flow rates through the PEG depositionchamber to maintain an inert atmosphere in the chamber. Silane isinjected “in the flow loop” which is heated and maintained at atemperature a little above the boiling point of silane. Vapors of thesilane are picked up by the running nitrogen. This is said to facilitatethe reaction on the silicon surface to form a thin organosilane film.Nitrogen is flowed through the deposition chamber to remove unreactedsilane. Ethylene oxide and boron trifluoride at a ratio of 1:2 weremaintained in the reaction chamber during deposition of the PEG film.(Page 647) The disclosure of this article is hereby incorporated byreference in its entirety. More details of this work are presented in aDoctor of Philosophy graduate thesis titled: “Development Of VaporDeposited Thin Films For Bio-Microsystems” by Ketul C. Popat, approvedat the University of Illinois at Chicago on Oct. 11, 2002, the contentof which is hereby incorporated by reference in its entirety.

Samuel K. Sia and George M. Whitesides, in their article entitled“Microfluidic devices fabricated in poly(dimethylsiloxane) forbiological studies”, in Electrophoresis 2003, 24, 3563-3576, describemicrofluidic systems in poly(dimethylsiloxane) (PDMS) for biologicalstudies. The properties of PDMS which make it a suitable platform forminiaturized biological studies, techniques for fabricating PDMSmicrostructures, and methods of controlling fluid flow in microchannelsare discussed. Biological procedures that are said to have beenminiaturized into PDMS-based microdevices are said to includeimmunoassays, separation of proteins and DNA, sorting and manipulationof cells, studies of cells in microchannels exposed to laminar flow offluids, and large-scale, combinatorial screening. The review emphasizesthe advantages of miniaturization for biological analysis, such asefficiency of the devices and insights into cell biology.

PDMS is described as consisting of repeating —OSi(CH₃)₂— units; the CH₃groups are said to make its surface hydrophobic. This hydrophobicity isdescribed as resulting in poor wettability with aqueous solvents, whichrenders microchannel devices susceptible to the trapping of air bubbles,and makes the surfaces of the microchannels prone to nonspecificadsorption to proteins and cells. The surface is said to be madehydrophilic by exposure to an air plasma; the plasma is said to oxidizethe surface of the PDMS to silanol(Si—OH). The plasma-oxidized surfaceis said to remain hydrophilic if it stays in contact with water. In air,rearrangements are said to occur within 30 minutes, which bringhydrophobic groups to the surface to lower the surface free energy. Itis mentioned that the surface of oxidized PDMS can be modified furtherby treatment with functionalized silanes. This article by Samuel Sia etal. is hereby incorporated by reference in its entirety.

U.S. Pat. No. 6,576,489 to Leung et al., issued Jun. 10, 2003, describesmethods of forming microstructure devices. The methods include the useof vapor-phase alkylsilane-containing molecules to form a coating over asubstrate surface. The alkylsilane-containing molecules are introducedinto a reaction chamber containing the substrate by bubbling ananhydrous, inert gas through a liquid source of thealkylsilane-containing molecules, and transporting the molecules withthe carrier gas into the reaction chamber. The formation of the coatingis carried out on a substrate surface at a temperature ranging betweenabout 15° C. and 100° C., at a pressure in the reaction chamber which issaid to be below atmospheric pressure, and yet sufficiently high for asuitable amount of alkylsilane-containing molecules to be present forexpeditious formation of the coating.

U.S. Patent Publication No. 2003/0180544 A1, published Sep. 25, 2003,and entitled “anti-Reflective Hydrophobic Coatings and Methods”,describes substrates having anti-reflective hydrophobic surfacecoatings. The coatings are typically deposited on a glass substrate. Asilicon oxide anchor layer is formed from a humidified reaction productof silicon tetrachloride, followed by the vapor deposition of achloroalkylsilane. The thickness of the anchor layer and the overlayerare said to be such that the coating exhibits light reflectance of lessthan about 1.5%. The coatings are said to be comprised of the reactionproducts of a vapor-deposited chlorosilyl group containing compound anda vapor-deposited alkylsilane.

U.S. Patent Publication No. US2004/0023413 A1, of Cindra Opalsky,published Feb. 5, 2004, describes the use of polyethylene glycol, or ablock co-polymer and/or derivative thereof which has been immobilized ona planar oxide surface that has been silanized. The immobilized moleculeis then used in a microscale screening or binding assay in an optimalhydrogel environment (Abstract). The polyethylene glycol is typicallyused in the form of a “hydrogel”, where the term hydrogel refers to agelatinous colloid or aggregate of molecules in a finely dispersedsemi-liquid state, where the molecules are in the external or dispersionphase and water is in the internal or dispersed phase. Preferredhydrogels are made using polyethylene glycol, polypropylene glycol orpolysine, or a derivative (such as a branched or star molecule) or blockco-polymer thereof. The immobilization or coupling of a hydrogel to asurface is typically carried out by contacting the hydrogel with asurface of interest to cause a physical or chemical reaction to occurbetween the hydrogel and the surface via one or more linkers. Forchemical attachment of the hydrogel to the surface, preferred surfacesinclude compositions containing oxides of silicon or tungsten. Inaddition, a silanized planar surface is also mentioned, where a surfacehaving hydroxyl groups present is reacted with an organo-silane compoundto create additional reactive groups for chemical coupling. Preferably,one or more linkers comprising the hydrogel are contacted with thesurface by depositing an aqueous solution directly onto the surface,which optionally may contain an intermediate layer to facilitatebinding. This reference is hereby incorporated by reference in itsentirety.

Other known related references pertaining to coatings deposited on asubstrate surface from a vapor include the following, as examples andnot by way of limitation. U.S. Pat. No. 5,576,247 to Yano et al., issuedNov. 19, 1996, entitled: “Thin layer forming method where hydrophobicmolecular layers preventing a BPSG layer from absorbing moisture”. U.S.Pat. No. 5,602,671 of Hornbeck, issued Feb. 11, 1997, which describeslow surface energy passivation layers for use in micromechanicaldevices. Jian Wang et al., in an article published in Thin Solid Films327-329 (1998) 591-594, entitled: “Gold nanoparticulate film bound tosilicon surface with self-assembled monolayers”, discuss a method forattaching gold nanoparticles to silicon surfaces with a self alignedmonolayer (SAM) used for surface preparation”.

Other known related references pertaining to coatings deposited on asubstrate surface from a vapor include the following, as examples andnot by way of limitation. U.S. Pat. No. 5,576,247 to Yano et al., issuedNov. 19, 1996, entitled: “Thin layer forming method where hydrophobicmolecular layers preventing a BPSG layer from absorbing moisture”. U.S.Pat. No. 5,602,671 of Hornbeck, issued Feb. 11, 1997, which describeslow surface energy passivation layers for use in micromechanicaldevices.

Some of the various methods useful in applying layers and coatings to asubstrate have been described above. There are numerous other patentsand publications which relate to the deposition of functional coatingson substrates, but which appear to us to be more distantly related tothe present invention. However, upon reading these informativedescriptions, it becomes readily apparent that control of coatingdeposition on a molecular level is not addressed in adequate detail inmost instances. When this is discussed, the process is typicallydescribed in generalized terms like those mentioned directly above,which terms are not enabling to one skilled in the art, but merelysuggest experimentation. To provide a monolayer or a few layers of afunctional coating on a substrate surface which is functional orexhibits features on a nanometer scale, it is necessary to tailor thecoating precisely. Without precise control of the deposition process,the coating may lack thickness uniformity and surface coverage,providing a rough surface. Or, the coating may vary in chemicalcomposition across the surface of the substrate. Or, the coating maydiffer in structural composition across the surface of the substrate.Any one of these non-uniformities may result in functionaldiscontinuities and defects on the coated substrate surface which areunacceptable for the intended application of the coated substrate.

U.S. patent application Ser. No. 10/759,857 of the present applicantsdescribes processing apparatus which can provide specificallycontrolled, accurate delivery of precise quantities of reactants to theprocess chamber, as a means of improving control over a coatingdeposition process. The subject matter of the '857 application is herebyincorporated by reference in its entirety. The focus of the presentapplication is the control of process conditions in the reaction chamberin a manner which, in combination with delivery of accurate quantitiesof reactive materials, provides a uniform, functional coating on ananometer scale. The coating exhibits sufficient uniformity ofthickness, chemical composition and structural composition over thesubstrate surface that such nanometer scale functionality is achieved.

SUMMARY OF THE INVENTION

We have developed an improved vapor-phase deposition method andapparatus for the application of layers and coatings on varioussubstrates. The method and apparatus are useful in the fabrication ofbiotechnologically functional devices, Bio-MEMS devices, and in thefabrication of microfluidic devices for biological applications. Thecoating formation method typically employs at least one stagnationreaction, and more typically a series of stagnation reactions. In eachstagnation reaction all of the reactants which are to be consumed arecharged to a vapor space over the substrate to be coated and are thenpermitted to react in a given process step, whether that step is one ina series of steps or is the sole step in a coating formation process. Insome instances, the coating formation process may include a number ofindividual steps where repetitive reactive processes are carried out ineach individual step. The apparatus used to carry out the methodprovides for the addition of a precise amount of each of the reactantsto be consumed in a single reaction step of the coating formationprocess. The apparatus may provide for precise addition of quantities ofdifferent combinations of reactants during each individual step whenthere are a series of different individual steps in the coatingformation process.

In addition to the control over the amount of reactants added to theprocess chamber, the present invention requires precise control over thecleanliness of the substrate, the order of reactant(s) introduction, thetotal pressure (which is typically less than atmospheric pressure) inthe process chamber, the partial vapor pressure of each vaporouscomponent present in the process chamber, and the temperature of thesubstrate and chamber walls. The control over this combination ofvariables determines the deposition rate and properties of the depositedlayers. By varying these process parameters, we control the amount ofthe reactants available, the density of reaction sites, and the filmgrowth rate, which is the result of the balance of the competitiveadsorption and desorption processes on the substrate surface, as well asany gas phase reactions.

The coating deposition process is carried out in a vacuum chamber wherethe total pressure is lower than atmospheric pressure and the partialpressure of each vaporous component making up the reactive mixture isspecifically controlled so that formation and attachment of molecules ona substrate surface are well controlled processes that can take place ina predictable manner, without starving the reaction from any of theprecursors. As previously mentioned, the surface concentration andlocation of reactive species are controlled using total pressure in theprocessing chamber, the kind and number of vaporous components presentin the process chamber, the partial pressure of each vaporous componentin the chamber, temperature of the substrate, temperature of the processchamber walls, and the amount of time that a given set of conditions ismaintained.

In some instances, where it is desired to have a particularly uniformgrowth of the composition across the coating surface, or a variablecomposition across the thickness of a multi-layered coating, more thanone batch of reactants may be charged to the process chamber duringformation of the coating.

An important aspect of the present invention is the surface preparationof the substrate prior to initiation of any deposition reaction on thesubstrate surface. The hydrophobicity of a given substrate surface maybe measured using a water droplet shape analysis method, for example.Silicon substrates, when treated with oxygen-containing plasmas, can befreed from organic contaminants and typically exhibit a water contactangle below 10°, indicative of a hydrophilic property of the treatedsubstrate. In the case of more hydrophobic substrates, such as, forexample, plastics or metals, the deposition or creation of every thinoxide layer on the substrate surface may be used to alter thehydrophobicity of the substrate surface. An oxide layer may comprisealuminum oxide, titanium oxide, or silicon oxide, by way of example andnot by way of limitation. When the oxide layer is aluminum or titaniumoxide, an auxiliary process chamber (to the process chamber describedherein) may be used to create this oxide layer. When the oxide layer isa silicon oxide layer, the silicon oxide layer may be applied by themethod of the present invention, to provide a more hydrophilic substratesurface, or the silicon oxide may act as an oxide bonding layer. Forexample, the oxide surface hydrophobicity can be adjusted downward to beas low as 5 degrees, rendering the surface hydrophilic.

As a part of a method for depositing specialized films, ultrathin oxidefilms are deposited on a multitude of substrates. Such oxide films canserve as a surface layer having controlled hydrophilic/hydrophobiccharacteristics, or may serve as a bonding, wetting, adhesion, or primerlayer (subsequently referred to as a “bonding” layer herein for generalpurposes of ease in description) for subsequently deposited variousmolecular coatings, including, for example, silane-basedsilicon-containing coatings.

By controlling the precise thickness, chemical, and structuralcomposition of an oxide layer on a substrate, for example, we are ableto tailor the oxide layer surface characteristics and thickness to abiological application. When the oxide serves as a bonding layer, we areable to direct the coverage and the functionality of a coating appliedover the bonding oxide layer. The coverage and functionality of thecoating can be controlled over the entire substrate surface on ananometer scale.

With reference to the application of chlorosilane-based coating systemsof the kind described in the Background Art section of this application,for example, and not by way of limitation, the degree of hydrophobicityof the substrate after deposition of an oxide bonding layer and afterdeposition of an overlying silane-based polymeric coating can beuniformly controlled over the substrate surface. By controlling adeposited bonding layer (for example) surface coverage and roughness ina uniform manner (as a function of oxide deposition parameters describedabove, for example and not by way of limitation), we are able to controlthe concentration of OH reactive species on the substrate surface. This,in turn, controls the density of reaction sites needed for subsequentdeposition of a silane-based polymeric coating. Control of the substratesurface active site density enables uniform growth and application ofhigh density self-aligned monolayer coatings (SAMS), for example.

By controlling the total pressure in the vacuum processing chamber, thenumber and kind of vaporous components charged to the process chamber,the partial pressure of each vaporous component, the substratetemperature, the temperature of the process chamber walls, and the timeover which particular conditions are maintained, the chemical reactivityand properties of the coating can be controlled. By controlling theprocess parameters, density of film coverage over the substrate surface;chemistry-dependent structural composition; film thickness; and filmuniformity over the substrate surface are more accurately controlled.Chemistry-dependent structural composition is most frequently generatedby use of a combination of layers, where different layers have adifferent chemical composition. Control over process parameters makespossible the formation of very smooth films, with RMS roughness whichtypically ranges from about 0.1 nm to less than about 15 nm, and evenmore typically from about 1 nm to about 5 nm. For oxide films used toprovide a hydrophilic surface, and/or used as a bonding layer, thethickness of the oxide film typically ranges from about 1 nm (10 Å) toabout 20 nm. Oxide films thicker than 20 nm (up to about 500 nm) areused when mechanical properties and film abrasion resistance are ofparticular importance. These films can be tailored in thickness,roughness, and density, which makes them particularly well suited forapplications in the field of biotechnology and electronics and asbonding layers for various functional coatings in general.

Oxide films deposited according to the present method can be used asbonding layers for subsequently deposited biocompatible coatingmaterials, such as (for example and not by way of limitation)polyethylene glycol (PEG). Polyethylene glycol is available in a widerange of molecular weights. The molecular weight of the polyethyleneglycol will determine its physical characteristics (e.g., as themolecular weight increases, viscosity and freezing point increase).Polyethylene glycol is also available with varying numbers of functional(i.e., binding) groups, such as monofunctional (one binding group),difunctional (two binding groups), and multi-functional (more than twobinding groups). The molecular weight and functionality of thepolyethylene glycol will in combination determine the particularapplications in which it is most useful. Polyethylene glycols which areuseful in the present method typically range from about 400 to about2000 in molecular weight.

Polyethylene glycol is commonly used in a wide range of industries,including electronics (e.g., printed circuit board manufacturing),electron microscopy, paper coating, textiles, wood processing, thecosmetics and toiletry industry, and in the medical/pharmaceuticalfield. Polyethylene glycol (with a structural formula: —(CH₂—CH₂—O)—) isa well-known, non-toxic class of polymers useful in biotechnological andbiomedical applications. For example, PEG is widely used as a drugcoating, and as a component of many medications (e.g. laxatives,ophthalmic solutions and others). It has been studied in blood andtissue engineering, as a material retarding bacterial growth and iswidely used as a coating in analytical tools and in medical devices suchas, for example, catheters or capillaries. PEG is known to behydrophilic and to reduce adsorption of protein and lipid cells due toits highly hydrated surface. In the present instance, PEG is applied forsurface treatment of substrates and devices which require hydrophilic,bio-compatible interfaces with body tissue and fluids or with biologicalreagents. Application of the PEG is by a molecular vapor depositionprocess performed in a vacuum. The application method steps include:

a) subjecting a surface which is planar or a surface having any one of avariety of three-dimensional shapes to an oxygen-comprising plasma in aprocessing chamber which is at a subatmospheric pressure. The pressuretypically ranges from about 0.01 Torr to about 1 Torr.

b) subsequently, without exposure of the oxygen-plasma-treated surfaceto ambient conditions which contaminate or react with the plasma-treatedsurface, exposing the surface to a silicon chloride-containing vapor inthe presence of moisture, to form a thin (2 nm to 20 nm thick),hydrophilic silicon oxide (siloxane) layer on the surface. The siliconchloride-containing vapor is preferably silicon tetrachloride.

c) subsequently, without exposure of the hydrophilic silicon oxide layerto ambient conditions which contaminate or react with the hydrophilicsilicon oxide layer, exposing the oxide layer to a functionalized silaneprecursor vapor containing PEO/PEG groups, to react these groups withthe hydrophilic silicon oxide layer, to form a layer selected from thegroup consisting of a monolayer, a self-aligned mono-layer, and apolymerized cross-linked layer.

Optionally, additional repetition of steps may be used, including astep:

d) repeating steps a) through c); or repeating steps b) through c); orrepeating step c) a nominal number of times without exposing thesubstrate to ambient contaminants.

Although just one layer of PEO/PEG may be applied, when it is desired toincrease the thickness of the PEO/PEG layer, step c) can be repeated.Typically, the PEO/PEG precursor may be charged to the reactor chamberand then pumped down to remove byproduct and unreacted precursormaterial in a series of steps to increase deposited layer thickness. Aseries of the charge and pump down steps in the range of about 2 toabout 10 is common, with a range of about 4 to about 8 being morecommon. Application of a series of add-on layers to increase the totalthickness of the deposited PEO/PEG layer improves the uniformity of thedeposited PEO/PEG layer over the surface of the substrate. It is notnecessary to plasma treat the surface of the existing PEO/PEG layerprior to charging additional reactant for deposition, since the surfaceof the existing PEO/PEG layer is easily bonded to by the newly chargedPEO/PEG layer precursor material.

When more than one precursor material is charged to the process chamberat one time, by changing the total pressure in the process chamberand/or limiting the partial pressure of a particular reactive vaporouscomponent so that the component is “starved” from the reactive substratesurface, a composition of a depositing coating can be “dialed in” tomeet particular requirements. When a single precursor material ischarged to the process chamber, by changing the total pressure in theprocess chamber and/or limiting the partial pressure of the reactivevaporous component, the surface coverage of the depositing coating canbe dialed in to meet particular hydrophobicity/hydrophylicityrequirements.

A computer-driven process control system may be used to provide for aseries of additions of reactants to the process chamber in which anindividual layer or a coating is being formed. This process controlsystem typically also controls other process variables, such as (forexample and not by way of limitation), total process chamber pressure(typically less than atmospheric pressure), substrate temperature,temperature of process chamber walls, temperature of the vapor deliverymanifolds, processing time for given process steps, and other processparameters if needed.

Oxide/polyethylene glycol (PEG) coatings providing hydrophilicity canalso be deposited, using the present method, over the surfaces ofvarious medical devices and implants, which are intended for varioustime periods of use. Internal devices such as smart bio-chips, which mayinclude internal diagnostic devices are excellent applications forcoated structures. External devices such as contact lenses, externaldiagnostic devices (including microfluidic devices), and catheters, forexample, provide excellent applications for coated structures. Coatedstructures which are intended for “permanent” (i.e., at least 5 to 10years) implantation within the body may include devices such asintra-ocular lenses, synthetic blood vessels and heart valves, stents,joint (such as a hip or knee) or hard tissue (i.e., bone or cartilage)replacements, and breast implants, for example and without limitation.The application of a hydrophilic oxide/PEG coating over surfaces of themedical device or implant improves both the hydrophilicity andbiocompatibility.

When the base substrate surface exhibits naturally strong hydrophobicsurface properties, such as PDMS, acrylic, and polystyrene, for exampleand not by way of limitation, treatment of the substrate surface toprovide hydrophilic characteristics which are maintained upon exposureto ambient air is difficult. Treatment of the strong hydrophobic surfacewith a low density, remotely-generated oxygen plasma alone provideshydrophilic characteristics initially, where a water droplet contactangle is about 5°; however, this contact angle increases to 63° afteronly one day. Treatment of the strong hydrophobic surface with ozone inthe presence of ultraviolet (UV) radiation, where the ozone is createdby the U.V. ionization of air, followed by treatment with the lowdensity oxygen plasma significantly improves the lifetime of thehydrophilic surface which has been created, where an increase in thewater droplet contact angle from about 7° to 60° requires about 6 days.An even better improvement in the lifetime of the hydrophilic surface,created by this latter treatment of the strongly hydrophobic basesubstrate surface, is achieved when a layer of PEG is applied over thetreated surface. Application of the PEG layer extends the time to about13 days for an increase in the water droplet contact angle from about13° to 60°. Preferably the layer of PEG is vapor deposited in the sameprocess chamber or at least without exposure to a harmful environmentafter surface treatment with ozone in the presence of ultraviolet (UVradiation).

The bonding of the PEG layer to a hydrophobic surface is improved whenthe surface has been treated with UV radiation in the presence of oxygenor ozone, to render the surface more hydrophilic and more compatiblewith PEG. The data presently available to us indicates that we have notyet been able to cover the entire surface of the treated substrate withPEG. A treated surface which is entirely covered with PEG shouldmaintain the 6° contact angle unless the PEG layer is damaged so thatunderlying substrate is exposed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional schematic of one embodiment of the kindof an apparatus which can be used to carry out a vapor deposition of acoating in accordance with the method of the present invention.

FIG. 2 is a schematic which shows the reaction mechanism wheretetrachlorosilane and water are reacted with a substrate which exhibitsactive hydroxyl groups on the substrate surface, to form a silicon oxidelayer on the surface of the substrate.

FIGS. 3A and 3B show schematics of atomic force microscope (AFM) imagesof silicon oxide bonding layers deposited on a silicon substrate. Theinitial silicon substrate surface RMS roughness measured less than about0.1 nm.

FIG. 3A shows the schematic for an AFM picture of a 4 nm thick siliconoxide bonding layer deposited from SiCl₄ precursor using the method ofthe present invention, where the RMS roughness is about 1.4 nm.

FIG. 3B shows the schematic for an AFM picture of a 30 nm thick siliconoxide bonding layer deposited from SiCl₄ precursor using the method ofthe present invention, where the RMS roughness is about 4.2 nm.

FIG. 4 shows a graph of the water contact angle (proportional topercentage of substrate surface coverage) as a function of time for acoating produced from a dimethyldichlorosilane precursor on the surfaceof a silicon substrate.

FIG. 5 shows a series of water contact angles measured for a coatingsurface where the coating was produced from a FOTS precursor on thesurface of a silicon substrate. The higher the contact angle, the higherthe hydrophobicity of the coating surface.

FIG. 6A shows a three dimensional schematic of film thickness of asilicon oxide bonding layer coating deposited on a silicon surface as afunction of the partial pressure of silicon tetrachloride and thepartial pressure of water vapor present in the process chamber duringdeposition of the silicon oxide coating, where the time period thesilicon substrate was exposed to the coating precursors was four minutesafter completion of addition of all precursor materials.

FIG. 6B shows a three dimensional schematic of film thickness of thesilicon oxide bonding layer illustrated in FIG. 6A as a function of thewater vapor partial pressure and the time period the substrate wasexposed to the coating precursors after completion of addition of allprecursor materials.

FIG. 6C shows a three dimensional schematic of film thickness of thesilicon oxide bonding layer illustrated in FIG. 6A as a function of thesilicon tetrachloride partial pressure and the time period the substratewas exposed to the coating precursors after completion of addition ofall precursor materials.

FIG. 7A shows a three dimensional schematic of film roughness in RMS nmof a silicon oxide bonding layer coating deposited on a silicon surfaceas a function of the partial pressure of silicon tetrachloride and thepartial pressure of water vapor present in the process chamber duringdeposition of the silicon oxide coating, where the time period thesilicon substrate was exposed to the coating precursors was four minutesafter completion of addition of all precursor materials.

FIG. 7B shows a three dimensional schematic of film roughness in RMS nmof the silicon oxide bonding layer illustrated in FIG. 7A as a functionof the water vapor partial pressure and the time period the substratewas exposed to the coating precursors after completion of addition ofall precursor materials.

FIG. 7C shows a three dimensional schematic of film roughness in RMS nmof the silicon oxide bonding layer illustrated in FIG. 6A as a functionof the silicon tetrachloride partial pressure and the time period thesubstrate was exposed to the coating precursors after completion ofaddition of all precursor materials.

FIG. 8A illustrates the change in hydrophilicity of the surface of theinitial substrate as a function of the thickness of an oxide-basedbonding layer generated over the initial substrate surface using anoxygen plasma, moisture, and carbon tetrachloride. When the oxidethickness is adequate to provide full coverage of the substrate surface,the contact angle on the surface drops to about 5 degrees or less.

FIG. 8B illustrates the minimum thickness of oxide-based bonding layerwhich is required to provide adhesion of an organic-based layer, as afunction of the initial substrate material, when the organic-based layeris one where the end or the organic-based layer which bonds to theoxide-based bonding layer is a silane and where the end of theorganic-based layer which does not bond to the oxide-based bonding layerprovides a hydrophobic surface. When the oxide thickness is adequate toprovide uniform attachment of the organic-based layer, the contact angleon the substrate surface increases to about 110 degrees or greater.

FIG. 9 shows stability in DI water for an organic-based self-aligningmonolayer (SAM) generated from perfluorodecyltrichloro-silane (FDTS)applied over an acrylic substrate surface; and, applied over a 150 Å (15nm) thick oxide-based layer, or applied over a 400 Å (40 nm) thickoxide-based layer, where the initial substrate surface is acrylic. Alsoshown is the improvement in long-term reliability and performance when aseries of five pairs of oxide-based layer/organic-based layer areapplied over the acrylic substrate surface.

FIG. 10A illustrates the improvement in DI water stability of anothermultilayered coating, where the organic-based precursor wasfluoro-tetrahydrooctyldimethylchlorosilanes (FOTS). The surfacestability of a FOTS organic-based layer applied directly over thesubstrate surface is compared with the surface stability of a FOTSorganic-based layer, which is the upper surface layer of a series ofalternating layers of oxide-based layer followed by organic based layer.FIG. 10A shows data for a silicon substrate surface.

FIG. 10B shows the same kind of comparison as shown in FIG. 10A;however, the substrate is glass.

FIG. 11A shows a 1536-well micro-plate, which is typically polystyreneor polypropylene with 1536 wells present in the substrate surface. Eachwell is about 1.5 to 2.0 mm in diameter and 5.0 mm deep. Typicalmicro-plate well aspect ratios may range from about 1:1 to about 4:1. InFIG. 11A, the hydrophobic polymeric surface of the polystyrene substratedoes not permit a sample drop to enter the well.

FIG. 11B shows the same 1536-well micro-plate, where a two layer coatinghaving an oxide bonding layer and a mono-functional PEG (mpEG) surfacelayer renders the hydrophobic micro-plate surface shown in FIG. 11Ahydrophilic, so that a fluid sample can more easily enter the well.

FIG. 12A shows a graph 1200 of the water droplet contact angle for aflat PDMS substrate surface in degrees on axis 1204, as a function ofthe amount of treatment time in minutes with ozone in the presence of UVradiation on axis 1202. Change in the contact angle over a period of 14days is also shown for the treated substrate, with the as-treated sampleshown in curve 1206, the one day exposure to ambient air at roomtemperature on curve 1208, two days' exposure on curve 1210, five days'exposure on curve 1212, seven days' exposure on curve 1216, and 14 days'exposure on curve 1218.

FIG. 12B shows a graph 1220 of the water droplet contact angle for aPDMS substrate on axis 1224, as a function of the amount of exposuretime of the substrate to ambient air at room temperature in days on axis1222. Curve 1226 is for a PDMS substrate surface treated with O₂ plasma,Curve 1228 is for a PDMS substrate surface treated with ozone in thepresence of UV radiation, and Curve 1230 is for a PDMS surface treatedwith ozone in the presence of UV radiation, followed by the applicationof an overlying layer of PEG.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As a preface to the detailed description, it should be noted that, asused in this specification and the appended claims, the singular forms“a”, “an”, and “the” include plural referents, unless the contextclearly dictates otherwise.

The use of “about” herein is intended to show that the value referred tois not an absolute limit, and may be within about ±10 percent of thenominal value recited.

As a basis for understanding the invention, it is necessary to discuss aprocessing apparatus which permits precise control over the addition ofcoating precursors and other vaporous components present within thereaction/processing chamber in which the coating is applied. Theapparatus described below is not the only apparatus in which the presentinvention may be practiced, it is merely an example of one apparatuswhich may be used. One skilled in the art will recognize equivalentelements in other forms which may be substituted and still provide anacceptable processing system.

Disclosed herein is a method of increasing the hydrophilicity of abiomedical device, where a surface of the device is vapor depositioncoated with a material having a hydrophilicity which is related to thesurface tension of a biological fluid which is present in or around thedevice. Fluids which are present in or around the implant or device aretypically hydrophilic (typically, water-based fluids), and a surface ofthe device is coated with a coating which increases the hydrophilicityof the device surface. The most common vapor-deposited coating used toincrease hydrophilicity include at least one oxide-based layer and atleast one organic functional layer, where an organic functional layerprovides the upper surface of the coating. When the organic functionallayer is a PEG-based layer, the vapor deposited coating typicallyexhibits a deionized water wetting angle ranging from about 5° or lessto about 60°; more typically, ranging from about 9° or less to about50°; most typically, ranging from about 15° or less to about 45°.

I. An Apparatus for Vapor Deposition of Thin Coatings

FIG. 1 shows a cross-sectional schematic of an apparatus 100 for vapordeposition of thin coatings. The apparatus 100 includes a processchamber 102 in which thin (typically 20 Å (2 nm) to 200 Å (20 nm)coatings, or thicker coatings in the range of about 200 Å (20 nm) toabout 1 micron thick (1,000 nm) may be vapor deposited. A substrate 106to be coated rests upon a temperature controlled substrate holder 104,typically within a recess 107 in the substrate holder 104.

Depending on the chamber design, the substrate 106 may rest on thechamber bottom (not shown in this position in FIG. 1). Attached toprocess chamber 102 is a remote plasma source 110, connected via a valve108. Remote plasma source 110 may be used to provide a plasma which isused to clean and/or convert a substrate surface to a particularchemical state prior to application of a coating (which enables reactionof coating species and/or catalyst with the surface, thus improvingadhesion and/or formation of the coating); or may be used to providespecies helpful during formation of the coating (not shown) ormodifications of the coating after deposition. The plasma may begenerated using a microwave, DC, or inductive RF power source, orcombinations thereof. The process chamber 102 makes use of an exhaustport 112 for the removal of reaction byproducts and is opened forpumping/purging the chamber 102. A shut-off valve or a control valve 114is used to isolate the chamber or to control the amount of vacuumapplied to the exhaust port. The vacuum source is not shown in FIG. 1.

The apparatus 100 shown in FIG. 1 is illustrative of a vapor depositedcoating which employs two precursor materials and a catalyst. Oneskilled in the art will understand that one or more precursors and fromzero to multiple catalysts may be used during vapor deposition of acoating. A catalyst storage container 116 contains catalyst 154, whichmay be heated using heater 118 to provide a vapor, as necessary. It isunderstood that precursor and catalyst storage container walls, andtransfer lines into process chamber 102 will be heated as necessary tomaintain a precursor or catalyst in a vaporous state, minimizing oravoiding condensation. The same is true with respect to heating of theinterior surfaces of process chamber 102 and the surface of substrate106 to which the coating (not shown) is applied. A control valve 120 ispresent on transfer line 119 between catalyst storage container 116 andcatalyst vapor reservoir 122, where the catalyst vapor is permitted toaccumulate until a nominal, specified pressure is measured at pressureindicator 124. Control valve 120 is in a normally-closed position andreturns to that position once the specified pressure is reached incatalyst vapor reservoir 122. At the time the catalyst vapor in vaporreservoir 122 is to be released, valve 126 on transfer line 119 isopened to permit entrance of the catalyst present in vapor reservoir 122into process chamber 102 which is at a lower pressure. Control valves120 and 126 are controlled by a programmable process control system ofthe kind known in the art (which is not shown in FIG. 1).

A Precursor 1 storage container 128 contains coating reactant Precursor1, which may be heated using heater 130 to provide a vapor, asnecessary. As previously mentioned, Precursor 1 transfer line 129 andvapor reservoir 134 internal surfaces are heated as necessary tomaintain a Precursor 1 in a vaporous state, minimizing and preferablyavoiding condensation. A control valve 132 is present on transfer line129 between Precursor 1 storage container 128 and Precursor 1 vaporreservoir 134, where the Precursor 1 vapor is permitted to accumulateuntil a nominal, specified pressure is measured at pressure indicator136. Control valve 132 is in a normally closed position and returns tothat position once the specified pressure is reached in Precursor 1vapor reservoir 134. At the time the Precursor 1 vapor in vaporreservoir 134 is to be released, valve 138 on transfer line 129 isopened to permit entrance of the Precursor 1 vapor present in vaporreservoir 134 into process chamber 102, which is at a lower pressure.Control valves 132 and 138 are controlled by a programmable processcontrol system of the kind known in the art (which is not shown in FIG.1).

A Precursor 2 storage container 140 contains coating reactant Precursor2, which may be heated using heater 142 to provide a vapor, asnecessary. As previously mentioned, Precursor 2 transfer line 141 andvapor reservoir 146 internal surfaces are heated as necessary tomaintain Precursor 2 in a vaporous state, minimizing, and preferablyavoiding condensation. A control valve 144 is present on transfer line141 between Precursor 2 storage container 146 and Precursor 2 vaporreservoir 146, where the Precursor 2 vapor is permitted to accumulateuntil a nominal, specified pressure is measured at pressure indicator148. Control valve 141 is in a normally-closed position and returns tothat position once the specified pressure is reached in Precursor 2vapor reservoir 146. At the time the Precursor 2 vapor in vaporreservoir 146 is to be released, valve 150 on transfer line 141 isopened to permit entrance of the Precursor 2 vapor present in vaporreservoir 146 into process chamber 102, which is at a lower pressure.Control valves 144 and 150 are controlled by a programmable processcontrol system of the kind known in the art (which is not shown in FIG.1).

During formation of a coating (not shown) on a surface 105 of substrate106, at least one incremental addition of vapor equal to the vaporreservoir 122 of the catalyst 154, and the vapor reservoir 134 of thePrecursor 1, or the vapor reservoir 146 of Precursor 2 may be added toprocess chamber 102. The total amount of vapor added is controlled byboth the adjustable volume size of each of the expansion chambers(typically 50 cc up to 1,000 cc) and the number of vapor injections(doses) into the reaction chamber. Further, the set pressure 124 forcatalyst vapor reservoir 122, or the set pressure 136 for Precursor 1vapor reservoir 134, or the set pressure 148 for Precursor 2 vaporreservoir 146, may be adjusted to control the amount (partial vaporpressure) of the catalyst or reactant added to any particular stepduring the coating formation process. This ability to control preciseamounts of catalyst and vaporous precursors to be dosed (charged) to theprocess chamber 102 at a specified time provides not only accuratedosing of reactants and catalysts, but repeatability in the vaporcharging sequence.

This apparatus provides a relatively inexpensive, yet accurate method ofadding vapor phase precursor reactants and catalyst to the coatingformation process, despite the fact that many of the precursors andcatalysts are typically relatively non-volatile materials. In the past,flow controllers were used to control the addition of various reactants;however, these flow controllers may not be able to handle some of theprecursors used for vapor deposition of coatings, due to the low vaporpressure and chemical nature of the precursor materials. The rate atwhich vapor is generated from some of the precursors is generally tooslow to function with a flow controller in a manner which providesavailability of material in a timely manner for the vapor depositionprocess.

The apparatus discussed above allows for accumulation of the specificquantity of vapor in the vapor reservoir which can be charged (dosed) tothe reaction. In the event it is desired to make several doses duringthe coating process, the apparatus can be programmed to do so, asdescribed above. Additionally, adding of the reactant vapors into thereaction chamber in controlled aliquots (as opposed to continuous flow)greatly reduces the amount of the reactants used and the cost of thecoating.

One skilled in the art of chemical processing of a number of substratessimultaneously will recognize that a processing system which permitsheat and mass transfer uniformly over a number of substrate surfacessimultaneously may be used to carry out the present invention.

II. Exemplary Embodiments of the Method of the Invention:

A method of the invention provides for vapor-phase deposition ofcoatings, where at least one processing chamber (including an expansionvolume and auxiliary valving and other apparatus) of the kind describedabove, or similar to the processing chamber described above is employed.Use of a processing chamber of the kind described in detail hereinpermits precise charging of vaporous reactive species which react with asubstrate surface under stagnated conditions. The kind of processingchamber which provides for stagnated reaction may be used in combinationwith other kinds of process chambers which permit a continuous flow ofreactant components across a substrate surface during coating deposition(not shown in drawings herein). This latter kind of processing chamberis commonly used in the art for chemical vapor deposition (CVD) of thinfilms, for example. A multi-chambered coating deposition system whichemploys a combination of the stagnation reaction processing chamber ofthe present invention with processing chambers of the kind used in theart for CVD, where substrates are moved between various processingchambers while the substrates are under a controlled environment, iscontemplated.

Use of the stagnated reaction condition processing chamber of the kinddescribed in detail herein permits precise charging of vaporous reactivespecies which react with a substrate surface under the stagnatedconditions. This reaction under stagnated reaction conditions isemployed during at least one individual deposition step to produce agiven deposited layer, or is employed during deposition of at least onelayer of a multilayered coating. Each coating precursor is transferredin vaporous form to a precursor vapor reservoir in which the precursorvapor accumulates. In the instance of simple, single-layer coatings, thevapor reservoir may be the processing chamber in which the coating isapplied. A nominal amount of the precursor vapor, which is the amountrequired for a coating layer deposition is accumulated in the precursorvapor reservoir. The at least one coating precursor is charged from theprecursor vapor reservoir into the processing chamber in which asubstrate to be coated resides. In some instances at least one catalystvapor is added to the process chamber in addition to the at least oneprecursor vapor, where the relative quantities of catalyst and precursorvapors are based on the physical characteristics to be exhibited by thecoating. In some instances a diluent gas is added to the process chamberin addition to the at least one precursor vapor (and optional catalystvapor). The diluent gas is chemically inert and is used to increase atotal desired processing pressure, while the partial pressure amounts ofcoating precursors and optionally catalyst components are varied.

The example embodiments described below are with reference to formationof oxide coatings which exhibit a controlled degree of hydrophilicity;or, are with reference to use of a bonding oxide layer with an overlyingsilane-based polymeric layer or a bonding oxide with an overlying PEGpolymeric layer to provide a hydrophobic surface on a substrate.However, it is readily apparent to one of skill in the art that theconcepts involved can be applied to additional coating compositions andcombinations which have different functionalities.

Due to the need to control the degree and scale of functionality of thecoating at dimensions as small as Angstroms or nanometers, the surfacepreparation of the substrate prior to application of the coating is veryimportant. One method of preparing the substrate surface is to exposethe surface to a uniform, non-physically-bombarding plasma which istypically created from a plasma source gas containing oxygen. The plasmamay be a remotely generated plasma which is fed into a processingchamber in which a substrate to be coated resides. Depending on thecoating to be applied directly over the substrate, the plasma treatmentof the substrate surface may be carried out in the chamber in which thecoating is to be applied. This has the advantage that the substrate iseasily maintained in a controlled environment between the time that thesurface is treated and the time at which the coating is applied.Alternatively, it is possible to use a large system which includesseveral processing chambers and a centralized transfer chamber whichallows substrate transfer from one chamber to another via a robothandling device, where the centralized handling chamber as well as theindividual processing chambers are each under a controlled environment.

To obtain the planned reaction on the initial, uncoated substratesurface, the initial substrate surface has to be prepared so that thereactivity of the surface itself with the vaporous components present inthe process chamber will be as expected. The treatment may be a wetchemical clean, but is preferably a plasma treatment. Typicallytreatment with an oxygen plasma removes common surface contaminants. Insome instances, it is necessary not only to remove contaminants from thesubstrate surface, but also to generate —OH functional groups on thesubstrate surface (in instances where such —OH functional groups are notalready present).

When a silicon oxide layer is applied to the substrate surface toprovide a substrate surface having a controlled hydrophobicity (acontrolled availability of reactive hydroxylated sites) orhydrophilicity, the oxide layer may be created using the well-knowncatalytic hydrolysis of a chlorosilane, such as a tetrachlorosilane, inthe manner previously described. A subsequent attachment of anorgano-chlorosilane, which may or may not include a functional moiety,may be made to impart a particular function to the finished coating. Byway of example and not by way of limitation, the hydrophobicity orhydrophilicity of the coating surface may be altered by the functionalmoiety present on a surface of an organo-chlorosilane which becomes theexterior surface of the coating.

The oxide layer, which may be silicon oxide or another oxide, may beformed using the method of the present invention by vapor phasehydrolysis of the chlorosilane, with subsequent attachment of thehydrolyzed silane to the substrate surface. Alternatively, thehydrolysis reaction may take place directly on the surface of thesubstrate, where moisture has been made available on the substratesurface to allow simultaneous hydrolyzation and attachment of thechlorosilane to the substrate surface.

By controlling the process parameters, both density of film coverageover the substrate surface and structural composition over the substratesurface are more accurately controlled, enabling the formation of verysmooth films, which typically range from about 0.1 nm to less than about15 nm, and even more typically from about 1 nm to about 5 nm in surfaceRMS roughness. For oxide films used to provide a hydrophilic surface,the thickness of the oxide film typically ranges from about 10 Å (1 nm)to about 200 Å (20 nm). When the oxide film is used as a structural(mechanically structural) and/or a bonding layer, the thickness of thelayer may be greater, typically up to about 1,000 nm (1.0μ), and moretypically up to about 500 nm (0.5μ). These films can be tailored inthickness, roughness, hydrophobicity/hydrophilicity, and density, whichmakes them particularly well suited for applications in the field ofbiotechnology and electronics. In addition, the structure of the filmscan be tailored to provide various functional coatings in general,particular where mechanical performance properties of the coatingstructure are important.

As previously discussed, oxide films deposited according to the presentmethod can be used as bonding layers for subsequently depositedbiocompatible coating materials, such as (for example and not by way oflimitation) polyethylene glycol (PEG). The molecular weight of thepolyethylene glycol will determine its physical characteristics (e.g.,as the molecular weight increases, viscosity and freezing pointincrease). Polyethylene glycol is also available with varying numbers offunctional (i.e., binding) groups, such as monofunctional (one bindinggroup), difunctional (two binding groups), and multi-functional (morethan two binding groups). The molecular weight and functionality of thepolyethylene glycol will in combination determine the particularapplications in which it is most useful. Polyethylene glycols which areuseful in the present method typically range from about 400 to about1000 in molecular weight.

Polyethylene glycol (with a structural formula: —(CH₂—CH₂—O)—) is awell-known, non-toxic class of polymers useful in biotechnological andbiomedical applications. For example, PEG is widely used as a drugcoating, and as a component of many medications (e.g. laxatives,ophthalmic solutions and others). It has been studied in blood and issueengineering, as a material retarding bacterial growth and is widely usedas a coating in analytical tools and in medical devices such as, forexample, catheters or capillaries. PEG is known to be hydrophilic and toreduce adsorption of protein and lipid cells due to its highly hydratedsurface. In the present instance, PEG is applied for surface treatmentof substrates and devices which require hydrophilic, bio-compatibleinterfaces with body tissue and fluids or with biological reagents.

EXAMPLE ONE

The vapor deposition techniques described previously herein were used tocoat devices such as implantable (intraocular) lenses with a hydrophilicoxide/polyethylene glycol coating. Prior to deposition of the coating,the device surface was pre-treated by exposure to an oxygen plasma(150-200 sccm O₂ at an RF power of about 200 W and a process chamberpressure of 0.3 Torr in an Applied MicroStructures' MVD™ processchamber) for 5 minutes in order to clean the surface and create hydroxylavailability on a substrate surface (by way of example and not by way oflimitation).

Following oxygen plasma treatment of the lens, SiCl₄ was charged to theprocess chamber from a SiCl₄ vapor reservoir, where the SiCl₄ vaporpressure in the vapor reservoir was 18 Torr, creating a partial pressureof 2.3 Torr in the coating process chamber. Within 5 seconds, a firstvolume of H₂O vapor was charged to the process chamber from a H₂O vaporreservoir, where the H₂O vapor pressure in the vapor reservoir was 18Torr. A total of five reservoir volumes of H₂O were charged, creating apartial pressure of 5.0 Torr in the coating process chamber. The totalpressure in the coating process chamber was 7.3 Torr. The substratetemperature and the temperature of the process chamber walls was about35° C. The substrate was exposed for a time period of about 10 minutesafter the final H₂O addition. The silicon oxide coating thicknessobtained was about 100 Å.

To apply the PEG coating, methoxy(polyethyleneoxy)propyltrimethoxysilane(Gelest P/N SIM6492.7) (MW=450-600), was charged to the process chamberfrom a PEG vapor reservoir, where the PEG vapor pressure in the vaporreservoir was about 500 mTorr. Four reservoir volumes of PEG werecharged, creating a partial pressure of 250 mTorr in the coating processchamber. After charging of the reservoir volumes, the substrate wasexposed to the PEG precursor vapor for a time period of 15 minutes. Nocharging of water vapor from a reservoir to the process chamber isnecessary with this PEG precursor. An alternative precursor which may beused to form a PEG coating ismethoxy(polyethyleneoxy)propyltrichlorosilane (Gelest P/N SIM6492.66).However, use of this PEG precursor requires the addition of water vapor.The temperature of the process chamber walls was within the range ofabout 25° C. to about 60° C., and was most typically about 35° C. ThePEG precursor source vessel and delivery line temperature was within therange of about 70° C. to about 110° C., and was most typically about100° C. The PEG coating thickness obtained was about 20 Å (2 nm).

It is contemplated that any ethyleneoxy (ethylene glycol) terminatedsilylated precursor (silane) with the functional groupR═HO(CH₂CH₂O)_(n)CH₂— could be used with the present vapor depositiontechniques, including, without limitation:

a chlorosilane or methoxysilane functionalized PEG-forming organosiliconderivative functionalized on either one or both PEG chain ends;

a poly(ethylene glycol) silane and bis-silane precursors; and

an alkyltrichlorosilane (RSiCl₃) or alkyltrimethoxysilane (RSi(OCH₃)₃precursor, where R contains ethylene glycol (oxide) groups.

Application of the PEG by a molecular vapor deposition process isperformed in a vacuum. The application method steps include:

a) subjecting a surface which is planar or a surface having any one of avariety of three-dimensional shapes to an oxygen-comprising plasma in aprocessing chamber which is at a subatmospheric pressure ranging fromabout 0.1 Torr to about 1.0 Torr;

b) subsequently, without prior exposure of the oxygen-plasma-treatedsurface to ambient conditions which contaminate or react with theplasma-treated surface, exposing the surface to a silicon tetrachloridevapor in the presence of moisture, to form a thin (2 nm to 20 nm thick),hydrophilic silicon oxide (siloxane) layer on the surface;

c) subsequently, without prior exposure of the hydrophilic silicon oxidelayer to ambient conditions which contaminate or react with thehydrophilic silicon oxide layer, exposing the oxide layer to afunctionalized silane precursor vapor containing PEO/PEG groups, toreact these groups with the hydrophilic silicon oxide layer, to form alayer selected from the group consisting of a monolayer, a self-alignedmono-layer, and a polymerized cross-linked layer.

Optionally, repetition of one or more of the above-recited steps may beused, where an additional step is carried out:

d) repeating steps a) through c); or b) through c); or just c) a nominalnumber of times without exposing the substrate to ambient contaminants.

Typical process conditions for steps a) through c) in a process chamberof the kind previously described (having a volume of about 1.5 to about2.0 liters) used in combination with a reservoir having a volume ofabout 300 cc are as follows. It is understood that one skilled in theart could adjust (scale) the process conditions provided below toaccommodate a larger or smaller process chamber or a larger or smallerreservoir. For manufacturing operations, the process chamber (andcoordinated reservoirs) would typically be considerably larger.

Step a): Plasma treatment of the substrate surface is carried out withan oxygen gas flow rate in the process chamber ranging from about 50sccm to about 400 sccm (when the process chamber volume is in the rangeof about 1.5-2.0 liters), with a process chamber pressure ranging fromabout 0.2 Torr to about 2.0 Torr. RF power to the plasma generationsource is in the range of about 100 W to about 300 W, and the treatmenttime is about 1 minute to about 10 minutes, typically about 5 minutes.

Step b): SiCl₄ vapor is injected from a vapor reservoir of approximately300 cc using an injection at a SiCl₄ vapor pressure of about 18 Torr.Subsequently, 5 injections of water vapor at 18 Torr from a vaporreservoir are added to the process chamber. In the alternative, a singleinjection of water vapor at 90 Torr may be used. The SiCl₄/water vaporcombination is permitted to react with the surface for a time periodranging from about 1 minute to about 30 minutes, typically about 10minutes. The film thickness may be adjusted by adjusting the amount oftime the reaction is permitted to proceed.

Step c): PEG-comprising precursor deposition is carried out at a processchamber temperature ranging from about 25° C. to about 40° C.,preferably at about 35° C. The PEG source and delivery line temperaturetypically ranges from about 70° C. to about 110° C., preferably thetemperature is about 100° C. PEG-comprising precursor and other reactantvapors are injected from a vapor reservoir of approximately 300 cc.

Typically about 4 injections of PEG-comprising precursor at 500 mTorrreservoir pressure are made. When water vapor is used, water vapor istypically injected at this time, by way of example and not by way oflimitation. The reaction time period for the PEG-comprising precursor orthe combination of reactants is in the range of about 5 minutes to 30minutes, typically about 15 minutes.

Two PEG-comprising precursors were evaluated,2-[methoxy(polyethyleneoxy)propyl] heptamethyltrisiloxane(C₁₁H₃₀O₃Si₃(C₂H₄O)₆₋₉CH₃; and

2-[methoxy(polyethyleneoxy)propyl]trimethoxysilane(CH₃(OC₂H₄)₆₋₉(CH₂)₃OSi(OCH3)₃. The resulting DI water contact angle ona substrate prepared in the manner described above, with respect to eachprecursor, was about 32 degrees on a silicon substrate and 22 degrees onan acrylic substrate.

Table 1 below provides test data for the silicon substrate and acrylicsubstrates in the form of lenses, with oxide and PEG-comprising coatinglayers applied in the manner described above.

TABLE 1 Acr Subst Si Subst flat Appearance PEG flat Contact Contact offive Run coating Angle Angle coated lenses Order SiO₂ (Å) cycles (°) (°)(transmission) 1 none 8 27 38 acceptable 2 20 4 8 26 acceptable 3 20 821 31 acceptable 4 60 4 26 23 acceptable 5 400 none <5 <5 not acceptable6 none 4 10 29 acceptable 7 none 2 7 32 acceptable 8 20 none <5 31acceptable 9 20 2 8 29 acceptable 10 150 none <5 <5 not acceptable 11 602 20 20 acceptable 12 60 8 28 28 not tested 13 none none <5 33 — 14 1504 26 19 acceptable 15 60 none <5 17 not tested 16 150 4 26 16 not tested

Oxide/polyethylene glycol coatings providing hydrophilicity can also bedeposited, using the present method, over the surfaces of other medicaldevices and implants, including those which are intended for temporaryuse (such as contact lenses and catheters, for example and withoutlimitation) and those which are intended for “permanent” (i.e., at least5 to 10 years) implantation (such as intra-ocular lenses, syntheticblood vessels and heart valves, stents, joint (such as a hip or knee) orhard tissue (i.e., bone or cartilage) replacements, and breast implants,for example and without limitation) within the body. The application ofa hydrophilic oxide/PEG coating over surfaces of the medical device orimplant improves both the hydrophilicity and biocompatibility of thedevice/implant.

In instances where it is desired to create multilayered coatings, forexample and not by way of limitation, it is advisable to use oxygenplasma treatment prior to and between PEO/PEG coating deposition steps.This oxygen plasma treatment activates dangling bonds on the substratesurface, which dangling bonds may be exposed to a controlled partialpressure of water vapor to create a new concentration of OH reactivesites on the substrate surface. The PEO/PEG coating deposition processmay then be repeated, increasing the coating thickness.

A computer-driven process control system may be used to provide for aseries of additions of reactants to the process chamber in which thelayer or coating is being formed. This process control system typicallyalso controls other process variables, such as (for example and not byway of limitation), total process chamber pressure (typically less thanatmospheric pressure), substrate temperature, temperature of processchamber walls, temperature of the vapor delivery manifolds, processingtime for given process steps, and other process parameters if needed.

The hydrolysis in the vapor phase using relatively wide range of partialpressure of the silicon tetrachloride precursor in combination with apartial pressure in the range of 10 Torr or greater of water vapor willgenerally result in rougher surfaces on the order of 5 nm RMS orgreater, where the thickness of the film formed will typically be in therange of about 20 nm or greater. Thinner films of the kind enabled byone of the embodiments of applicants' invention typically exhibit a 1-5m RMS finish and are grown by carefully balancing the vapor and surfacehydrolysis reaction components. For example, and not by way oflimitation, for a thin film of an oxide-based layer, prepared on asilicon substrate, where the oxide-based layer exhibits a thicknessranging from about 2 nm to about 15 nm, typically the oxide-based layerexhibits a 1-5 nm RMS finish.

We have obtained such films in an apparatus of the kind previouslydescribed, where the partial pressure of the silicon tetrachloride is inthe range of about 0.5 to 4.0 Torr, the partial pressure of the watervapor is in the range of about 2 to about 8 Torr, where the totalprocess chamber pressure ranges from about 3 Torr to about 10 Torr,where the substrate temperature ranges from about 20° C. to about 60°C., where the process chamber walls are at a temperature ranging fromabout 30° C. to about 60° C., and where the time period over which thesubstrate is exposed to the combination of silicon tetrachloride andwater vapor ranges from about 2 minutes to about 12 minutes. Thisdeposition process will be described in more detail subsequently herein,with reference to FIGS. 6A through 6C.

A multilayered coating process may include plasma treatment of thesurface of one deposited layer prior to application of an overlyinglayer. Typically, the plasma used for such treatment is a low densityplasma. This plasma may be a remotely generated plasma. The mostimportant feature of the treatment plasma is that it is a “soft” plasmawhich affects the exposed surface enough to activate the surface of thelayer being treated, but not enough to etch through the layer. Theapparatus used to carry out the method provides for the addition of aprecise amount of each of the reactants to be consumed in a singlereaction step of the coating formation process. The apparatus mayprovide for precise addition of different combinations of reactantsduring each individual step when there are a series of differentindividual steps in the coating formation process. Some of theindividual steps may be repetitive.

One example of the application of the method described here isdeposition of a multilayered coating including at least one oxide-basedlayer. The thickness of the oxide-based layer depends on the end-useapplication for the multilayered coating. The oxide-based layer (or aseries of oxide-based layers alternated with organic-based layers) maybe used to increase the overall thickness of the multilayered coating(which typically derives the majority of its thickness from theoxide-based layer), and depending on the mechanical properties to beobtained, the oxide-based layer content of the multilayered coating maybe increased when more coating rigidity and abrasion resistance isrequired.

The oxide-based layer is frequently used to provide a bonding surfacefor subsequently deposited various molecular organic-based coatinglayers. When the surface of the oxide-based layer is one containing —OHfunctional groups, the organic-based coating layer typically includes,for example and not by way of limitation, a silane-based functionalitywhich permits covalent bonding of the organic-based coating layer to —OHfunctional groups present on the surface of the oxide-based layer. Whenthe surface of the oxide-based layer is one capped with halogenfunctional groups, such as chlorine, by way of example and not by way oflimitation, the organic-based coating layer includes, for example, an—OH functional group, which permits covalent bonding of theorganic-based coating layer to the oxide-based layer functional halogengroup.

By controlling the precise thickness, chemical, and structuralcomposition of an oxide-based layer on a substrate, for example, we areable to direct the coverage and the functionality of a coating appliedover the bonding oxide layer. The coverage and functionality of thecoating can be controlled over the entire substrate surface on a nmscale. Specific, different thicknesses of an oxide-based substratebonding layer are required on different substrates. Some substratesrequire an alternating series of oxide-based/organic-based layers toprovide surface stability for a coating structure.

With respect to substrate surface properties, such as hydrophobicity orhydrophilicity, for example, a silicon wafer surface becomeshydrophilic, to provide a less than 5 degree water contact angle, afterplasma treatment when there is some moisture present. Not much moistureis required, for example, typically the amount of moisture present afterpumping a chamber from ambient air down to about 15 mTorr to 20 mTorr issufficient moisture. A stainless steel surface requires formation of anoverlying oxide-based layer having a thickness of about 30 Å or more toobtain the same degree of hydrophilicity as that obtained by plasmatreatment of a silicon surface. Glass and polystyrene materials becomehydrophilic, to a 5 degree water contact angle, after the application ofabout 80 Å or more of an oxide-based layer. An acrylic surface requiresabout 150 Å or more of an oxide-based layer to provide a 5 degree watercontact angle.

There is also a required thickness of oxide-based layer to provide agood bonding surface for reaction with a subsequently appliedorganic-based layer. By a good bonding surface, it is meant a surfacewhich provides full, uniform surface coverage of the organic-basedlayer. By way of example, about 80 Å or more of a oxide-based substratebonding layer over a silicon wafer substrate provides a uniformhydrophobic contact angle, about 112 degrees, upon application of a SAMorganic-based layer deposited from an FDTS(perfluorodecyltrichlorosilanes) precursor. About 150 Å or more ofoxide-based substrate bonding layer is required over a glass substrateor a polystyrene substrate to obtain a uniform coating having a similarcontact angle. About 400 Å or more of oxide-based substrate bondinglayer is required over an acrylic substrate to obtain a uniform coatinghaving a similar contact angle.

The organic-based layer precursor, in addition to containing afunctional group capable of reacting with the oxide-based layer toprovide a covalent bond, may also contain a functional group at alocation which will form the exterior surface of the attachedorganic-based layer. This functional group may subsequently be reactedwith other organic-based precursors, or may be the final layer of thecoating and be used to provide surface properties of the coating, suchas to render the surface hydrophobic or hydrophilic, by way of exampleand not by way of limitation. The functionality of an attachedorganic-based layer may be affected by the chemical composition of theprevious organic-based layer (or the chemical composition of the initialsubstrate) if the thickness of the oxide layer separating the attachedorganic-based layer from the previous organic-based layer (or othersubstrate) is inadequate. The required oxide-based layer thickness is afunction of the chemical composition of the substrate surface underlyingthe oxide-based layer, as illustrated above. In some instances, toprovide structural stability for the surface layer of the coating, it isnecessary to apply several alternating layers of an oxide-based layerand an organic-based layer.

With reference to chlorosilane-based coating systems of the kinddescribed in the Background Art section of this application, where oneend of the organic molecule presents chlorosilane, and the other end ofthe organic molecule presents a fluorine moiety, after attachment of thechlorosilane end of the organic molecule to the substrate, the fluorinemoiety at the other end of the organic molecule provides a hydrophobiccoating surface. Further, the degree of hydrophobicity and theuniformity of the hydrophobic surface at a given location across thecoated surface may be controlled using the oxide-based layer which isapplied over the substrate surface prior to application of thechlorosilane-comprising organic molecule. By controlling the oxide-basedlayer application, the organic-based layer is controlled indirectly. Forexample, using the process variables previously described, we are ableto control the concentration of OH reactive species on the substratesurface. This, in turn, controls the density of reaction sites neededfor subsequent deposition of a silane-based polymeric coating. Controlof the substrate surface active site density enables uniform growth andapplication of high density self-aligned monolayer coatings (SAMS), forexample.

We have discovered that it is possible to convert a hydrophilic-likesubstrate surface to a hydrophobic surface by application of anoxide-based layer of the minimal thickness described above with respectto a given substrate, followed by application of an organic-based layerover the oxide-based layer, where the organic-based layer provideshydrophobic surface functional groups on the end of the organic moleculewhich does not react with the oxide-based layer. However, when theinitial substrate surface is a hydrophobic surface and it is desired toconvert this surface to a hydrophilic surface, it is necessary to use astructure which comprises more than one oxide-based layer to obtainstability of the applied hydrophilic surface in water. It is not justthe thickness of the oxide-based layer or the thickness of theorganic-based layer which is controlling. The structural stabilityprovided by a multilayered structure of repeated layers of oxide-basedmaterial interleaved with organic-based layers provides excellentresults.

After deposition of a first organic-based layer, and prior to thedeposition of a subsequent layer in a multilayered coating, it isadvisable to use an in-situ oxygen plasma treatment. This treatmentactivates reaction sites of the first organic-based layer and may beused as part of a process for generating an oxide-based layer or simplyto activate dangling bonds on the substrate surface. The activateddangling bonds may be exploited to provide reactive sites on thesubstrate surface. For example, an oxygen plasma treatment incombination with a controlled partial pressure of water vapor may beused to create a new concentration of OH reactive species on an exposedsurface. The activated surface is then used to provide covalent bondingwith the next layer of material applied. A deposition process may thenbe repeated, increasing the total coating thickness, and eventuallyproviding a surface layer having the desired surface properties. In someinstances, where the substrate surface includes metal atoms, treatmentwith the oxygen plasma and moisture provides a metal oxide-based layercontaining —OH functional groups. This oxide-based layer is useful forincreasing the overall thickness of the multilayered coating and forimproving mechanical strength and rigidity of the multilayered coating.

Following the deposition of a multilayered coating as described above, asurface oxide layer can be used as a bonding layer for subsequentdeposition of biocompatible coating materials, such as (for example andnot by way of limitation) polyethylene glycol (PEG). Polyethylene glycolcan be deposited using molecular vapor deposition (MVD™) to provide asurface layer over underling layers of other materials.

EXAMPLE TWO

Deposition of a Silicon Oxide Layer Having a Controlled Number of OHReactive Sites Available on the Oxide Layer Surface

A technique for adjusting the hydrophobicity/hydrophilicity of asubstrate surface (so that the surface is converted from hydrophobic tohydrophilic or so that a hydrophilic surface is made more hydrophilic,for example) may also be viewed as adjusting the number of OH reactivesites available on the surface of the substrate. One such technique isto apply an oxide coating over the substrate surface while providing thedesired concentration of OH reactive sites available on the oxidesurface. A schematic 200 of the mechanism of oxide formation in shown inFIG. 2. In particular, a substrate 202 has OH groups 204 present on thesubstrate surface 203. A chlorosilane 208, such as the tetrachlorosilaneshown, and water 206 are reacted with the OH groups 204, eithersimultaneously or in sequence, to produce the oxide layer 205 shown onsurface 203 of substrate 202 and byproduct HCl 210. In addition tochlorosilane precursors, chlorosiloxanes, fluorosilanes, andfluorosiloxanes may be used.

Subsequently, the surface of the oxide layer 205 can be further reactedwith water 216 to replace C1 atoms on the upper surface of oxide layer205 with OH groups 217, to produce the hydroxylated layer 215 shown onsurface 203 of substrate 202 and byproduct HCl 220. By controlling theamount of water used in both reactions, the frequency of OH reactivesites available on the oxide surface is controlled.

EXAMPLE THREE

In the preferred embodiment discussed below, the silicon oxide coatingwas applied over a glass substrate. The glass substrate was treated withan oxygen plasma in the presence of residual moisture which was presentin the process chamber (after pump down of the chamber to about 20mTorr) to provide a clean surface (free from organic contaminants) andto provide the initial OH groups on the glass surface.

Various process conditions for the subsequent reaction of the OH groupson the glass surface with vaporous tetrachlorosilane and water areprovided below in Table 2, along with data related to the thickness androughness of the oxide coating obtained and the contact angle(indicating hydrophobicity/hydrophilicity) obtained under the respectiveprocess conditions. A lower contact angle indicates increasedhydrophilicity and an increase in the number of available OH groups onthe silicon oxide surface.

TABLE 2 Deposition of a Silicon Oxide Layer of Varying HydrophilicityPartial Partial Pressure Pressure Coating SiO₂ SiCl₄ H₂O ReactionCoating Roughness Contact Order of Vapor Vapor Time Thickness (RMS,Angle*** Run No. Dosing (Torr) (Torr) (min.) (nm) nm)* (°) 1 First² 0.84 10 3 1 <5 SiCl₄ 2 First¹ 4 10 10 35 5 <5 H₂O 3 First² 4 10 10 30 4 <5SiCl₄ Partial Partial FOTS Pressure Pressure Coating Surface FOTS H₂OReaction Coating Roughness Contact Order of Vapor Vapor Time Thickness(RMS, Angle*** Dosing (Torr) (Torr) (min.) (nm)** nm)* (°) 1 First³ 0.20.8 15 4 1 108 FOTS 2 First³ 0.2 0.8 15 36 5 109 FOTS 3 First³ 0.2 0.815 31 4 109 FOTS *Coating roughness is the RMS roughness measured by AFM(atomic force microscopy). **The FOTS coating layer was a monolayerwhich added ≈1 nm in thickness. ***Contact angles were measured with 18MΩ D.I. water. ¹The H₂O was added to the process chamber 10 secondsbefore the SiCl₄ was added to the process chamber. ²The SiCl₄ was addedto the process chamber 10 seconds before the H₂O was added to theprocess chamber. ³The FOTS was added to the process chamber 5 secondsbefore the H₂O was added to the process chamber. ⁴The substratetemperature and the chamber wall temperature were each 35° C. for bothapplication of the SiO₂ bonding/bonding layer and for application of theFOTS organo-silane overlying monolayer (SAM) layer.

We have discovered that very different film thicknesses and film surfaceroughness characteristics can be obtained as a function of the partialpressures of the precursors, despite the maintenance of the same timeperiod of exposure to the precursors. Table 3 below illustrates thisunexpected result.

TABLE 3 Response Surface Design* Silicon Oxide Layer DepositionSubstrate Partial Partial and Coating Pressure Pressure Chamber SurfaceTotal SiCl₄ H₂O Wall Reaction Coating Roughness Pressure Vapor VaporTemp. Time Thickness RMS Run No. (Torr) (Torr) (Torr) (° C.) (min.) (nm)(nm) 1 9.4 2.4 7 35 7 8.8 NA 2 4.8 0.8 4 35 7 2.4 1.29 3 6.4 2.4 4 35 43.8 1.39 4 14 4 10 35 7 21.9 NA 5 7.8 0.8 7 35 4 4 2.26 6 11 4 7 35 109.7 NA 7 11 4 7 35 4 10.5 NA 8 12.4 2.4 10 35 4 14 NA 9 6.4 2.4 4 35 104.4 1.39 10 9.4 2.4 7 35 7 8.7 NA 11 12.4 2.4 10 35 10 18.7 NA 12 9.42.4 7 35 7 9.5 NA 13 8 4.8 4 35 7 6.2 2.16 14 10.8 0.8 10 35 7 6.9 NA 157.8 0.8 7 35 10 4.4 2.24 *(Box-Behnken) 3 Factors, 3 Center Points NA =Not Available, Not Measured

In addition to the tetrachlorosilane described above as a precursor foroxide formation, other chlorosilane precursors such a trichlorosilanes,dichlorosilanes work well as a precursor for oxide formation. Examplesof specific advantageous precursors include hexachlorodisilane (Si₂Cl₆)and hexachlorodisiloxane (Si₂Cl₆O). As previously mentioned, in additionto chlorosilanes, chlorosiloxanes, fluorosilanes, and fluorosiloxanesmay also be used as precursors.

Similarly, the vapor deposited silicon oxide coating from the SiCl₄ andH₂O precursors was applied over glass, polycarbonate, acrylic,polyethylene and other plastic materials using the same processconditions as those described above with reference to the siliconsubstrate. Prior to application of the silicon oxide coating, thesurface to be coated was treated with an oxygen plasma.

A silicon oxide coating of the kind described above can be applied overa self aligned monolayer (SAM) coating formed from an organic precursor,for example and not by way of limitation fromfluoro-tetrahydrooctyldimethylchlorosilane (FOTS). Prior to applicationof the silicon oxide coating, the surface of the SAM should be treatedwith an oxygen plasma. A FOTS coating surface requires a plasmatreatment of about 10-30 seconds to enable adhesion of the silicon oxidecoating. The plasma treatment creates reactive OH sites on the surfaceof the SAM layer, which sites can subsequently be reacted with SiCl₄ andwater precursors, as illustrated in FIG. 2, to create a silicon oxidecoating. This approach allows for deposition of multi-layered molecularcoatings, where all of the layers may be the same, or some of the layersmay be different, to provide particular performance capabilities for themulti-layered coating.

Functional properties designed to meet the end use application of thefinalized product can be tailored by either sequentially adding anorgano-silane precursor to the oxide coating precursors or by using anorgano-silane precursor(s) for formation of the last, top layer coating.Organo-silane precursor materials may include functional groups suchthat the silane precursor includes an alkyl group, an alkoxyl group, analkyl substituted group containing fluorine, an alkoxyl substitutedgroup containing fluorine, a vinyl group, an ethynyl group, or asubstituted group containing a silicon atom or an oxygen atom, by way ofexample and not by way of limitation. In particular, organic-containingprecursor materials such as (and not by way of limitation) silanes,chlorosilanes, fluorosilanes, methoxy silanes, alkyl silanes, aminosilanes, epoxy silanes, glycoxy silanes, and acrylosilanes are useful ingeneral.

Some of the particular precursors used to produce coatings are, by wayof example and not by way of limitation, perfluorodecyltrichlorosilanes(FDTS), undecenyltrichlorosilanes (UTS), vinyl-trichlorosilanes (VTS),decyltrichlorosilanes (DTS), octadecyltrichlorosilanes (OTS),dimethyldichlorosilanes (DDMS), dodecenyltricholrosilanes (DDTS),fluoro-tetrahydrooctyldimethylchlorosilanes (FOTS),perfluorooctyldimethylchlorosilanes, aminopropylmethoxysilanes (APTMS),fluoropropylmethyldichlorosilanes, andperfluorodecyldimethylchlorosilanes. The OTS, DTS, UTS, VTS, DDTS, FOTS,and FDTS are all trichlorosilane precursors. The other end of theprecursor chain is a saturated hydrocarbon with respect to OTS, DTS, andUTS; contains a vinyl functional group, with respect to VTS and DDTS;and contains fluorine atoms with respect to FDTS (which also hasfluorine atoms along the majority of the chain length). Other usefulprecursors include 3-aminopropyltrimethoxysilane (APTMS), which providesamino functionality, and 3-glycidoxypropyltrimethoxysilane (GPTMS). Oneskilled in the art of organic chemistry can see that the vapor depositedcoatings from these precursors can be tailored to provide particularfunctional characteristics for a coated surface.

Most of the silane-based precursors, such as commonly used di- andtri-chlorosilanes, for example and not by way of limitation, tend tocreate agglomerates on the surface of the substrate during the coatingformation. These agglomerates can cause structure malfunctioning orstiction. Such agglomerations are produced by partial hydrolysis andpolycondensation of the polychlorosilanes. This agglomeration can beprevented by precise metering of moisture in the process ambient whichis a source of the hydrolysis, and by carefully controlled metering ofthe availability of the chlorosilane precursors to the coating formationprocess. The carefully metered amounts of material and carefultemperature control of the substrate and the process chamber walls canprovide the partial vapor pressure and condensation surfaces necessaryto control formation of the coating on the surface of the substraterather than promoting undesired reactions in the vapor phase or on theprocess chamber walls.

EXAMPLE FOUR

When the oxide-forming silane and the organo-silane which includes thefunctional moiety are deposited simultaneously (co-deposited), thereaction may be so rapid that the sequence of precursor addition to theprocess chamber becomes critical. For example, in a co-depositionprocess of SiCl₄/FOTS/H₂O, if the FOTS is introduced first, it depositson the glass substrate surface very rapidly in the form of islands,preventing the deposition of a homogeneous composite film. Examples ofthis are provided in Table 4, below.

When the oxide-forming silane is applied to the substrate surface first,to form the oxide layer with a controlled density of potential OHreactive sites available on the surface, the subsequent reaction of theoxide surface with a FOTS precursor provides a uniform film without thepresence of agglomerated islands of polymeric material, examples of thisare provided in Table 4 below.

TABLE 4 Deposition of a Coating Upon a Silicon Substrate* Using SiliconTetrachloride and FOTS Precursors Partial Partial Partial SubstratePressure Pressure Pressure and Chamber Total SiCl₄ FOTS H₂O WallPressure Vapor Vapor Vapor Temp. Run No. (Torr) (Torr) (Torr) (Torr) (°C.) 1 FOTS + H₂O 1 — 0.2 0.8 35 2 H₂O + SiCl₄ 141 4 — 100.8 3535  followed by —  0.20   FOTS + H₂O 3 FOTS + SiCl₄ + H₂O 14.2 4 0.2 10 35 4SiCl₄ + H₂O 14 4 — 10 35 5 SiCl₄ + H₂O 5.8 0.8 — 5 35 6 SiCl₄ + H₂O 14 4— 10 35   repeated twice Coating Reaction Coating Roughness Contact TimeThickness (nm)** Angle*** (min.) (nm) RMS (°) 1 15 0.7 0.1 110 2 10 + 1535.5 4.8 110 3 15 1.5 0.8 110 4 10 30 0.9 <5 5 10 4 0.8 <5 6 10 + 10 551 <5 *The silicon substrates used to prepare experimental samplesdescribed herein exhibited an initial surface RMS roughness in the rangeof about 0.1 nm, as measured by Atomic Force Microscope (AFM). **Coatingroughness is the RMS roughness measured by AFM. ***Contact angles weremeasured with 18 MΩ D.I. water.

An example process description for Run No. 2 was as follows.

Step 1. Pump down the reactor and purge out the residual air andmoisture to a final baseline pressure of about 30 mTorr or less.

Step 2. Perform O₂ plasma clean of the substrate surface to eliminateresidual surface contamination and to oxygenate/hydroxylate thesubstrate. The cleaning plasma is an oxygen-containing plasma. Typicallythe plasma source is a remote plasma source, which may employ aninductive power source. However, other plasma generation apparatus maybe used. In any case, the plasma treatment of the substrate is typicallycarried out in the coating application process chamber. The plasmadensity/efficiency should be adequate to provide a substrate surfaceafter plasma treatment which exhibits a contact angle of about 10° orless when measured with 18 MΩ D.I. water. The coating chamber pressureduring plasma treatment of the substrate surface in the coating chamberwas 0.5 Torr, and the duration of substrate exposure to the plasma was 5minutes.

Step 3. Inject SiCl₄ and within 10 seconds inject water vapor at aspecific partial pressure ratio to the SiCl₄, to form a silicon oxidebase layer on the substrate. For example, for the glass substratediscussed in Table III, 1 volume (300 cc at 100 Torr) of SiCl₄ to apartial pressure of 4 Torr was injected, then, within 10 seconds 10volumes (300 cc at 17 Torr each) of water vapor were injected to producea partial pressure of 10 Torr in the process chamber, so that thevolumetric pressure ratio of water vapor to silicon tetrachloride isabout 2.5. The substrate was exposed to this gas mixture for 1 min to 15minutes, typically for about 10 minutes. The substrate temperature inthe examples described above was in the range of about 35° C. Substratetemperature may be in the range from about 20° C. to about 80° C. Theprocess chamber surfaces were also in the range of about 35° C.

Step 4. Evacuate the reactor to <30 mTorr to remove the reactants.

Step 5. Introduce the chlorosilane precursor and water vapor to form ahydrophobic coating. In the example in Table III, FOTS vapor wasinjected first to the charging reservoir, and then into the coatingprocess chamber, to provide a FOTS partial pressure of 200 mTorr in theprocess chamber, then, within 10 seconds, H₂O vapor (300 cc at 12 Torr)was injected to provide a partial pressure of about 800 mTorr, so thatthe total reaction pressure in the chamber was 1 Torr. The substrate wasexposed to this mixture for 5 to 30 minutes, typically 15 minutes, wherethe substrate temperature was about 35° C. Again, the process chambersurface was also at about 35° C.

An example process description for Run No. 3 was as follows.

Step 1. Pump down the reactor and purge out the residual air andmoisture to a final baseline pressure of about 30 mTorr or less.

Step 2. Perform remote O₂ plasma clean to eliminate residual surfacecontamination and to oxygenate/hydroxylate the glass substrate. Processconditions for the plasma treatment were the same as described abovewith reference to Run No. 2.

Step 3. Inject FOTS into the coating process chamber to produce a 200mTorr partial pressure in the process chamber. Then, inject 1 volume(300 cc at 100 Torr) of SiCl₄ from a vapor reservoir into the coatingprocess chamber, to a partial pressure of 4 Torr in the process chamber.Then, within 10 seconds, inject ten volumes (300 cc at 17 Torr each) ofwater vapor from a vapor reservoir into the coating process chamber, toa partial pressure of 10 Torr in the coating process chamber. Totalpressure in the process chamber is then about 14 Torr. The substratetemperature was in the range of about 35° C. for the specific examplesdescribed, but could range from about 15° C. to about 80° C. Thesubstrate was exposed to this three gas mixture for about 1-15 minutes,typically about 10 minutes.

Step 4. Evacuate the process chamber to a pressure of about 30 mTorr toremove excess reactants.

EXAMPLE FIVE

FIGS. 3A and 3B are schematics of AFM (atomic force microscope) imagesof surfaces of silicon oxide bonding coatings as applied over a siliconsubstrate. The initial silicon substrate surface RMS roughness wasdetermined to be less than about 0.1 nm. FIG. 3A illustrates adeposition process in which the substrate was silicon. The surface ofthe silicon was exposed to an oxygen plasma in the manner previouslydescribed herein for purposes of cleaning the surface and creatinghydroxyl availability on the silicon surface. SiCl₄ was charged to theprocess chamber from a SiCl₄ vapor reservoir, creating a partialpressure of 0.8 Torr in the coating process chamber. Within 10 seconds,H₂O vapor was charged to the process chamber from a H₂O vapor reservoir,creating a partial pressure of 4 Torr in the coating process chamber.The total pressure in the coating process chamber was 4.8 Torr. Thesubstrate temperature and the temperature of the process chamber wallswas about 35° C. The substrate was exposed to the mixture of SiCl₄ andH₂O for a time period of 10 minutes. The silicon oxide coating thicknessobtained was about 3 nm. The coating roughness in RMS was 1.4 nm and Rawas 0.94 nm.

FIG. 3B illustrates a deposition process in which the substrate wassilicon. The surface of the silicon was exposed to an oxygen plasma inthe manner previously described herein for purposes of cleaning thesurface and creating hydroxyl availability on the silicon surface. SiCl₄was charged to the process chamber from a SiCl₄ vapor reservoir,creating a partial pressure of 4 Torr in the coating process chamber.Within 10 seconds, H₂O vapor was charged to the process chamber from aH₂O vapor reservoir, creating a partial pressure of 10 Torr in thecoating process chamber. The total pressure in the coating processchamber was 14 Torr. The substrate temperature and the temperature ofthe process chamber walls was about 35° C. The substrate was exposed tothe mixture of SiCl₄ and H₂O for a time period of 10 minutes. Thesilicon oxide coating thickness obtained was about 30 nm. The coatingroughness in RMS was 4.2 nm and Ra was 3.4 nm.

EXAMPLE SIX

FIG. 4 shows a graph 400 of the dependence of the water contact angle(an indication of hydrophobicity of a surface) as a function of thesubstrate exposure time for a silicon substrate coated directly with anorgano-silane coating generated from a DDMS (dimethyldichlorosilane)precursor. The silicon substrate was cleaned and functionalized toprovide surface hydroxyl groups by an oxygen plasma treatment of thekind previously described herein. DDMS was then applied at a partialpressure of 1 Torr, followed within 10 seconds by H₂O applied at apartial pressure of 2 Torr, to produce a total pressure within theprocess chamber of 3 Torr.

In FIG. 4, graph 400, the substrate exposure period with respect to theDDMS and H₂O precursor combination is shown in minutes on axis 402, withthe contact angle shown in degrees on axis 404. Curve 406 illustratesthat it is possible to obtain a wide range of hydrophobic surfaces bycontrolling the process variables in the manner of the presentinvention. The typical standard deviation of the contact angle was lessthan 2 degrees across the substrate surface. Both wafer-to wafer andday-to day repeatability of the water contact angle were within themeasurement error of ±2° for a series of silicon samples.

FIG. 5 illustrates contact angles for a series of surfaces exposed towater, where the surfaces exhibited different hydrophobicity, with anincrease in contact angle representing increased hydrophobicity. Thisdata is provided as an illustration to make the contact angle datapresented in tables herein more meaningful.

EXAMPLE SEVEN

FIG. 6A shows a three dimensional schematic 600 of film thickness of asilicon oxide bonding layer coating deposited on a silicon surface as afunction of the partial pressure of silicon tetrachloride and thepartial pressure of water vapor present in the process chamber duringdeposition of the silicon oxide coating, where the temperature of thesubstrate and of the coating process chamber walls was about 35° C., andthe time period the silicon substrate was exposed to the coatingprecursors was four minutes after completion of addition of allprecursor materials. The precursor SiCl₄ vapor was added to the processchamber first, with the precursor H₂O vapor added within 10 secondsthereafter. The partial pressure of the H₂O in the coating processchamber is shown on axis 602, with the partial pressure of the SiCl₄shown on axis 604. The film thickness is shown on axis 606 in Angstroms.The film deposition time after addition of the precursors was 4 minutes.The thinner coatings exhibited a smoother surface, with the RMSroughness of a coating at point 608 on Graph 600 being in the range of 1nm (10 Å). The thicker coatings exhibited a rougher surface, which wasstill smooth relative to coatings generally known in the art. At point610 on Graph 600, the RMS roughness of the coating was in the range of 4nm (40 Å). FIG. 7A shows a three dimensional schematic 700 of the filmroughness in RMS, m which corresponds with the coated substrate forwhich the coating thickness is illustrated in FIG. 6A. The partialpressure of the H₂O in the coating process chamber is shown on axis 702,with the partial pressure of the SiCl₄ shown on axis 704. The filmroughness in RMS, nm is shown on axis 706. The film deposition timeafter addition of all of the precursors was 7 minutes. As previouslymentioned, the thinner coatings exhibited a smoother surface, with theRMS roughness of a coating at point 708 being in the range of 1 mm (10Å) and the roughness at point 710 being in the range of 4 nm (40 Å).

FIG. 6B shows a three dimensional schematic 620 of film thickness of thesilicon oxide bonding layer illustrated in FIG. 6A as a function of thewater vapor partial pressure and the time period the substrate wasexposed to the coating precursors after completion of addition of allprecursor materials. The time period of exposure of the substrate isshown on axis 622 in minutes, with the H₂O partial pressure shown onaxis 624 in Torr, and the oxide coating thickness shown on axis 626 inAngstroms. The partial pressure of SiCl₄ in the silicon oxide coatingdeposition chamber was 0.8 Torr.

FIG. 6C shows a three dimensional schematic 640 of film thickness of thesilicon oxide bonding layer illustrated in FIG. 6A as a function of thesilicon tetrachloride partial pressure and the time period the substratewas exposed to the coating precursors after completion of addition ofall precursor materials. The time period of exposure is shown on axis642 in minutes, with the SiCl₄ partial pressure shown on axis 646 inTorr, and the oxide thickness shown on axis 646 in Angstroms. The H₂Opartial pressure in the silicon oxide coating deposition chamber was 4Torr.

A comparison of FIGS. 6A-6C makes it clear that it is the partialpressure of the H₂O which must be more carefully controlled in order toensure that the desired coating thickness is obtained.

FIG. 7B shows a three dimensional schematic 720 of film roughness of thesilicon oxide bonding layer illustrated in FIG. 6B as a function of thewater vapor partial pressure and the time period the substrate wasexposed to the coating precursors after completion of addition of allprecursor materials. The time period of exposure of the substrate isshown on axis 722 in minutes, with the H₂O partial pressure shown onaxis 724 in Torr, and the surface roughness of the silicon oxide layershown on axis 726 in RMS, nm. The partial pressure of the SiCl₄ in thesilicon oxide coating deposition chamber was 2.4 Torr.

FIG. 7C shows a three dimensional schematic 740 of film roughnessthickness of the silicon oxide bonding layer illustrated in FIG. 6A as afunction of the silicon tetrachloride partial pressure and the timeperiod the substrate was exposed to the coating precursors aftercompletion of addition of all precursor materials. The time period ofexposure is shown on axis 742 in minutes, with the SiCl₄ partialpressure shown on axis 744 in Torr, and the surface roughness of thesilicon oxide layer shown on axis 746 in RMS, nm. The partial pressureof the H₂O in the silicon oxide coating deposition chamber was 7.0 Torr.

A comparison of FIGS. 7A-7C makes it clear that it is the partialpressure of the H₂O which must be more carefully controlled in order toensure that the desired roughness of the coating surface is obtained.

FIG. 8A is a graph 800 which shows the hydrophilicity of an oxide-basedlayer on different substrate materials, as a function of the thicknessof the oxide-based layer. The data presented in FIG. 8A indicates thatto obtain full surface coverage by the oxide-based layer, it isnecessary to apply a different thickness of oxide-based layer dependingon the underlying substrate material.

In particular, the oxide-based layer was a silicon-oxide-based layerprepared in general in the manner described above, with respect to RunNo. 4 in Table III, but where the nominal amounts of reactants chargedand/or reaction time of the reactants were varied to provide the desiredsilicon oxide layer thickness, which is specified on axis 802 of FIG.8A. The graph 800 shows the contact angle for a deionized (DI) waterdroplet, in degrees, on axis 804, as measured for a given oxide-basedlayer surface, as a function of the thickness of the oxide-based layerin Angstroms shown on axis 802. Curve 806 illustrates asilicon-oxide-based layer deposited over a single crystal silicon wafersurface. Curve 808 represents a silicon-oxide-based layer deposited overa soda lime glass surface. Curve 810 illustrates a silicon-oxide-basedlayer deposited over a stainless steel surface. Curve 812 shows asilicon-oxide-based layer deposited over a polystyrene surface. Curve814 illustrates a silicon-oxide-based layer deposited over an acrylicsurface.

Graph 800 shows that a single crystal silicon substrate required onlyabout a 30 Å thick coating of a silicon oxide-based layer to provide aDI water droplet contact angle of about 5 degrees, indicating themaximum hydrophilicity typically obtained using a silicon oxide-basedlayer. The glass substrate required about 80 Å of the siliconoxide-based layer to provide a contact angle of about 5 degrees. Thestainless steel substrate required a silicon oxide-based layer thicknessof about 80 Å to provide the contact angle of 5 degrees. The polystyrenesubstrate required a silicon oxide-based layer thickness of about 80 Åto provide the contact angle of 5 degrees. And, the acrylic substraterequired a silicon oxide-based layer thickness of about 150 Å. It shouldbe mentioned that the hydrophilicity indicated in FIG. 8A was measuredimmediately after completion of the coating process, since the nominalvalue measured may change during storage.

FIG. 8B shows a graph 820, which illustrates the relationship betweenthe hydrophobicity obtained on the surface of a SAM layer deposited fromperfluorodecyltrichlorosilane (FDTS), as a function of the thickness ofan oxide-based layer over which the FDTS layer was deposited. The oxidelayer was deposited in the manner described above, usingtetrachlorosilane precursor, with sufficient moisture that a siliconoxide surface having sufficient hydroxyl groups present to provide asurface contact angle (with a DI water droplet) of 5 degrees wasproduced.

The oxide-based layer and the organic-based layer generated from an FDTSprecursor were deposited as follows: The process chamber was vented andthe substrate was loaded into the chamber. Prior to deposition of theoxide-based layer, the surface of the substrate was plasma cleaned toeliminate residual surface contamination and to oxygenate/hydroxylatethe substrate. The chamber was pumped down to a pressure in the range ofabout 30 mTorr or less. The substrate surface was then plasma treatedusing a low density, non-physically-bombarding plasma which was createdexternally from a plasma source gas containing oxygen. The plasma wascreated in an external chamber which is a high efficiency inductivelycoupled plasma generator, and was fed into the substrate processingchamber. The plasma treatment was in the manner previously describedherein, where the processing chamber pressure during plasma treatmentwas in the range of about 0.5 Torr, the temperature in the processingchamber was about 35° C., and the duration of substrate exposure to theplasma was about 5 minutes.

After plasma treatment, the processing chamber was pumped down to apressure in the range of about 30 mTorr or less to evacuate remainingoxygen species. Optionally, processing chamber may be purged withnitrogen up to a pressure of about 10 Torr to about 20 Torr and thenpumped down to the pressure in the range of about 30 mTorr. An adheringoxide-based layer was then deposited on the substrate surface. Thethickness of the oxide-based layer depended on the substrate material,as previously discussed. SiCl₄ vapor was injected into the processchamber at a partial pressure to provide a desired nominal oxide-basedlayer thickness. To produce an oxide-based layer thickness ranging fromabout 30 Å to about 400 Å, typically the partial pressure in the processchamber of the SiCl₄ vapor ranges from about 0.5 Torr to about 4 Torr,more typically from about 1 Torr to about 3 Torr. Typically, withinabout 10 seconds of injection of the SiCl₄ vapor, water vapor wasinjected at a specific partial pressure ratio to the SiCl₄ to form theadhering silicon-oxide based layer on the substrate. Typically thepartial pressure of the water vapor ranges from about 2 Torr to about 8Torr, and more typically from about 4 Torr to about 6 Torr. (Severalvolumes of SiCl₄ and/or several volumes of water may be injected intothe process chamber to achieve the total partial pressures desired, aspreviously described herein.) The reaction time to produce the oxidelayer may range from about 5 minutes to about 15 minutes, depending onthe processing temperature, and in the exemplary embodiments describedherein the reaction time used was about 10 minutes at about 35° C.

After deposition of the oxide-based layer, the chamber was once againpumped down to a pressure in the range of about 30 mTorr or less.Optionally, the processing chamber may be purged with nitrogen up to apressure of about 10 Torr to about 20 Torr and then pumped down to thepressure in the range of about 30 mTorr, as previously described. Theorganic-based layer deposited from an FDTS precursor was then producedby injecting FDTS into the process chamber to provide a partial pressureranging from about 30 mTorr to about 1500 mTorr, more typically rangingfrom about 100 mTorr to about 300 mTorr. The exemplary embodimentsdescribed herein were typically carried out using an FDTS partialpressure of about 150 mTorr. Within about 10 seconds after injection ofthe FDTS precursor, water vapor was injected into the process chamber toprovide a partial pressure of water vapor ranging from about 300 mTorrto about 1000 mTorr, more typically ranging from about 400 mTorr toabout 800 mTorr. The exemplary embodiments described herein weretypically carried out using a water vapor partial pressure of about 600mTorr. The reaction time for formation of the organic-based layer (aSAM) ranged from about 5 minutes to about 30 minutes, depending on theprocessing temperature, more typically from about 10 minutes to about 20minutes, and in the exemplary embodiments described herein the reactiontime used was about 15 minutes at about 35° C.

The data presented in FIG. 8B indicates that to obtain the maximumhydrophobicity at the surface of the FDTS-layer, it is not onlynecessary to have an oxide-based layer thickness which is adequate tocover the substrate surface, but it is also necessary to have a thickerlayer in some instances, depending on the substrate underlying theoxide-based layer Since the silicon oxide layer is conformal, it wouldappear that the increased thickness is not necessary to compensate forroughness, but has a basis in the chemical composition of the substrate.However, as a matter of interest, the initial roughness of the siliconwafer surface was about 0.1 RMS nm, and the initial roughness of theglass surface was about 1-2 RMS nm.

In particular, the oxide-based layer was a silicon-oxide-based layerprepared in the manner described above, with respect to FIG. 8A. Thegraph 820 shows the contact angle of a DI water droplet, in degrees, onaxis 824, as measured for an oxide-based layer surface over differentsubstrates, as a function of the thickness of the oxide-based layer inAngstroms shown on axis 822. Curve 826 illustrates a silicon-oxide-basedlayer deposited over a single crystal silicon wafer surface describedwith reference to FIG. 8A. Curve 828 represents a silicon-oxide-basedlayer deposited over a glass surface as described with reference to FIG.8A. Curve 830 illustrates a silicon-oxide-based layer deposited over astainless steel surface, as described with reference to FIG. 8A. Curve832 shows a silicon-oxide-based layer deposited over a polystyrenesurface, as described with reference to FIG. 8A. Curve 834 illustrates asilicon-oxide-based layer deposited over an acrylic surface describedwith reference to FIG. 8A. The FDTS-generated SAM layer provides anupper surface containing fluorine atoms, which is generally hydrophobicin nature. The maximum contact angle provided by thisfluorine-containing upper surface is about 117 degrees. As illustratedin FIG. 8B, this maximum contact angle, indicating an FDTS layercovering the entire substrate surface is only obtained when theunderlying oxide-based layer also covers the entire substrate surface ata particular minimum thickness. There appears to be another factor whichrequires a further increase in the oxide-based layer thickness, over andabove the thickness required to fully cover the substrate, with respectto some substrates. It appears this additional increase in oxide-layerthickness is necessary to fully isolate the surface organic-based layer,a self-aligned-monolayer (SAM), from the effects of the underlyingsubstrate. It is important to keep in mind that the thickness of the SAMdeposited from the FDTS layer is only about 10 Å to about 20 Å.

Graph 820 shows that a SAM surface layer deposited from FDTS over asingle crystal silicon substrate exhibits the maximum contact angle ofabout 117 degrees when the oxide-based layer overlying the singlecrystal silicon has a thickness of about 30 Å or greater. The surfacelayer deposited from FDTS over a glass substrate exhibits the maximumcontact angle of about 117 degrees when the oxide-based layer overlyingthe glass substrate has a thickness of about 150 Å or greater. Thesurface layer deposited from FDTS over the stainless steel substrateexhibits the maximum contact angle of about 117 degrees when theoxide-based layer overlying the stainless steel substrate has athickness of between 80 Å and 150 Å or greater. The surface layerdeposited from FDTS over the polystyrene substrate exhibits the maximumcontact angle when the oxide-based layer overlying the polystyrenesubstrate has a thickness of 150 Å or greater. The surface layerdeposited from FDTS over the acrylic substrate exhibits the maximumcontact angle when the oxide-based layer overlying the acrylic substratehas a thickness of 400 Å or greater.

FIG. 9 illustrates the stability of the hydrophobic surface provided bythe SAM surface layer deposited from FDTS, when the coated substrate isimmersed in deionized (DI) water for a specified time period. Each testspecimen was plasma treated, then coated with oxide and SAM depositedfrom an FDTS precursor. Each test specimen size was about 1 cm² on thetwo major surfaces, and was coated on all sides. Each specimen wasimmersed into distilled water present in a 6 inch diameter round glassdish, without any means for circulating the water around the sample, andwas allowed to stand in the water at atmospheric pressure and at roomtemperature (about 27° C.). After the time period specified, eachspecimen was blown dry using a gentle nitrogen gas sparging; there wasno baking of the test specimens. After drying, a DI contact angle wasmeasured on the test specimen surface using the contact angle testmethod previously described herein, which is generally known in the art.

FIG. 9 shows a graph 980 which illustrates the stability of anapproximately 15 Å thick layer of a SAM deposited from FDTS over anacrylic substrate without and with various oxide coatings applied overthe acrylic substrate surface. Curve 986 shows the contact angle whenthe SAM was applied directly over the acrylic substrate. Curve 988 showsthe contact angle for a test specimen where a 150 Å thick silicon oxidelayer was applied over the acrylic substrate surface prior toapplication of the SAM layer. Curve 990 shows the contact angle for atest specimen where a 400 Å thick silicon oxide layer was applied overthe acrylic substrate surface prior to application of the SAM layer.While increasing the thickness of the oxide layer helped to increase theinitial hydrophobic properties of the substrate surface (indicatingimproved bonding of the SAM layer or improved surface coverage by theSAM layer), the structure was not stable, as indicated by the change incontact angle over time. In an effort to provide a more stablestructure, we applied a multilayered structure over the acrylicsubstrate, with the multilayered structure including a series of fivepairs of oxide-based layer/organic-based layer, to provide anorganic-based surface layer. Curve 992 shows the stability of thehydrophobic surface layer obtained when this multilayered structure wasapplied. This indicates that it is possible to provide a stablestructure which can withstand extended periods of water immersion bycreating the multilayered structure described. The number of pairs(sets) of oxide-based layer/organic-based layer which are requireddepends on the substrate material. When the substrate material isacrylic, the number of sets of oxide-based layer/organic-based layerwhich should be used is approximately five sets or more. For othersubstrate materials, the number of sets of oxide-basedlayer/organic-based layer may be fewer; however, use of at least twosets of layers helps provide a more mechanically stable structure.

The stability of the deposited SAM organic-based layers can be increasedby baking for about one half hour at 110° C., to crosslink theorganic-based layers. Baking of a single pair of layers is not adequateto provide the stability which is observed for the multilayeredstructure, but baking can even further improve the performance of themultilayered structure.

The integrated method for creating a multilayered structure of the kinddescribed above includes: Treatment of the substrate surface to removecontaminants and to provide either —OH or halogen moieties on thesubstrate surface, typically the contaminants are removed using a lowdensity oxygen plasma, or ozone, or ultra violet (UV) treatment of thesubstrate surface. The —OH or halogen moieties are commonly provided bydeposition of an oxide-based layer in the manner previously describedherein. A first SAM layer is then vapor deposited over the oxide-basedlayer surface. The surface of the first SAM layer is then treated usinga low density isotropic oxygen plasma, where the treatment is limited tojust the upper surface of the SAM layer, with a goal of activating thesurface of the first SAM. layer. It is important not to etch away theSAM layer down to the underlying oxide-based layer. By adjusting theoxygen plasma conditions and the time period of treatment, one skilledin the art will be able to activate the first SAM layer surface whileleaving the bottom portion of the first SAM layer intact. Typically, thesurface treatment is similar to a substrate pretreatment, where thesurface is treated with the low density isotropic oxygen plasma for atime period ranging from about 25 seconds to about 60 seconds, andtypically for about 30 seconds. In the apparatus described herein thepretreatment is carried out by pumping the process chamber to a pressureranging from about 15 mTorr to about 20 mTorr, followed by flowing anexternally-generated oxygen-based plasma into the chamber at a plasmaprecursor oxygen flow rate of about 50 sccm to 200 sccm, typically atabout 150 sccm in the apparatus described herein, to create about 0.4Torr in the substrate processing chamber.

After activation of the surface of the first SAM layer using theoxygen-based plasma, a second oxide-based layer is vapor deposited overthe first sam layer. A second SAM layer is then vapor deposited over thesecond oxide-based layer. The second SAM layer is then plasma treated toactivate the surface of the second SAM layer. The process of depositionof oxide-based layer followed by deposition of SAM layer, followed byactivation of the SAM surface may be repeated a nominal number of timesto produce a multilayered structure which provides the desiredmechanical strength and surface properties. Of course there typically isno activation step after deposition of the final surface layer of themultilayered structure, where the surface properties desired are thoseof the final organic-based layer. It is important to mention that thefinal organic-based layer may be different from other organic-basedlayers in the structure, so that the desired mechanical properties forthe structure may be obtained, while the surface properties of the finalorganic-based layer are achieved. The final surface layer is typically aSAM layer, but may also be an oxide-based layer.

As described previously herein, the thickness and roughness of theinitial oxide-based layer can be varied over wide ranges by choosing thepartial pressure of precursors, the temperature during vapor deposition,and the duration time of the deposition. Subsequent oxide-based layerthicknesses may also be varied, where the roughness of the surface maybe adjusted to meet end use requirements. The thickness of anorganic-based layer which is applied over the oxide-based layer willdepend on the precursor molecular length of the organic-based layer. Inthe instance where the organic-based layer is a SAM, such as FOTS, forexample, the thickness of an individual SAM layer will be in the rangeof about 15 Å. The thicknesses for a variety of SAM layers are known inthe art. Other organic-based layer thicknesses will depend on thepolymeric structure which is deposited using polymer vapor depositiontechniques. The organic-based layers deposited may be different fromeach other, and may present hydrophilic or hydrophobic surfaceproperties of varying degrees. In some instances, the organic-basedlayers may be formed from a mixture of more than one precursor. In someinstances, the organic-based layer may be vapor deposited simultaneouslywith an oxide-based structure to provide crosslinking of organic andinorganic materials and the formation of a dense, essentiallypinhole-free structure.

EXAMPLE EIGHT

FIGS. 10A and 10B provide comparative examples which further illustratethe improvement in structure stability and surface properties for a SAMwhich is deposited from a FOTS precursor over a multilayered structureof the kind described above (with respect to a SAM deposited from FDTS).

FIG. 10A shows a graph 1000 which illustrates the improvement in DIwater stability of a SAM when the organic-based precursor wasfluoro-tetrahydrooctyldimethylchlorosilanes (FOTS) and the multilayeredstructure described was present beneath the FOTS based SAM layer. Curve1008 shows physical property data (contact angle with a DI waterdroplet) for an approximately 800 Å thick layer of a SAM deposited fromFOTS directly upon a single crystal silicon substrate which was oxygenplasma pre-treated in the manner previously described herein. The DIwater droplet contact angle is shown on axis 1004 in degrees; the numberof days of immersion of the substrate (with overlying oxide and SAMlayer in place) is shown on axis 1002 in days. For a silicon substrate(which provides a hydrophilic surface), with the FOTS applied directlyover the substrate, the stability of the organic-based SAM layer, interms of the hygroscopic surface provided, decreases gradually from aninitial contact angle of about 108° to a contact angle of less thanabout 90° after a 14 day time period, as illustrated by curve 1006.

This decrease in contact angle compares with a decrease in contact anglefrom about 110° to about 105° over the 14 day time period, when thestructure is a series of five pairs of silicon oxide/FOTS SAM layers,with a SAM surface layer, as illustrated by curve 1008.

FIG. 10B shows a graph 1020 illustrating stability in DI water for thesame FOTS organic-based SAM layer applied directly over the substrate orapplied over a series of five pairs of silicon oxide/FOTS SAM layers,when the substrate is soda lime glass. The DI water droplet contactangle is shown on axis 1024 in degrees; the number of days of immersionof the substrate (with overlying oxide and SAM layer in place) is shownon axis 1022 in days.

When the FOTS SAM layer was applied directly over the substrate, thestability of the organic-based SAM layer, in terms of the hygroscopicsurface provided, decreased gradually from an initial contact angle ofabout 98° to a contact angle of less than about 88° after a 14 day timeperiod, as illustrated by curve 1026. This compares with a decrease incontact angle from about 108° to about 107° over the 14 day time period,when the structure is a series of five pairs of silicon oxide/FOTS SAMlayers, as illustrated by curve 1028.

EXAMPLE NINE

FIGS. 11A and 11B show schematic views of the top surfaces of highthroughput screening (HTS) micro-plates, where water droplets wereapplied to small wells in the plates. FIG. 11A illustrates the abilityof the water droplet to flow into the wells in the plate with no coatingon the polystyrene substrate of the screening plate. FIG. 11Billustrates the ability of the water drop to flow into the wells in theplate when a 150 Å thick oxide layer was applied by molecular vapordeposition (MVD™, Applied MicroStructures, Inc., San Jose, Calif.) overthe polystyrene surface, followed by MVD™ of a layer of biocompatible,monofunctional PEG (mPEG) at a thickness of about 20 Å.

In particular, precise control of liquid volume and flow in testingmicro-arrays is critical to the accuracy and consistency of analyticalresults achieved from such testing.

The material to be tested, typically a water-based material, is pipetted(commonly by robot) into very small channels (wells) formed within ascreening plate.

For example, a 1536-well screening micro-plate typically measures about130 mm×85 mm×10 mm (L×W×H) and contains 1536 small wells. In a 1536-wellscreening micro-plate, a well typically has a volume of about 12 μl. Amicro-plate well normally has a diameter ranging from about 1.0 mm toabout 2.0 mm and extends to a depth ranging from about 1.0 mm deep toabout 5.0 mm deep. As a result, the aspect ratio (the depth of the welldivided by the diameter of the well) of a well ranges from about 0.5:1to about 5:1. Typically, an aspect ratio ranges from about 2:1 to about4:1.

Most micro-plates are made of very hydrophobic materials, such aspolystyrene or polypropylene, each of which has a water contact angle ofaround 100°. Water readily beads up on these materials, making itdifficult to fill narrow wells formed within micro-plates made from suchhydrophobic materials. The difficulty in filling these wells will becomemore severe in future micro-plates with higher well density.

The droplet size of a droplet of water-based material applied to eachwell often ranges from about 1 mm to about 3 mm. Allowing for even smallamounts of imprecision in application of a droplet of water-basedmaterial, it is apparent why a droplet may trap air in the well and sitat the top of the well. This occurred when the polystyrene substrate ofthe micro-plate 1100 (shown in FIG. 11A) was not prepared by the methodof the invention, as illustrated by bubbles 1102 of the water-basedmaterial droplets on the upper surface 1103 of micro-plate 1100 at eachwell 1104.

FIG. 11B shows how the water-based material flowed into the wells in themicro-plate 1110, to provide a relatively flush upper surface 1112 ofthe water-based material on the upper surface 1113 of micro-plate 1110at each well 1114.

The droplets of water-based material were comprised of deionized water.The micro-plate polystyrene substrates were at 25° C., and the length oftime permitted for the water-based material to flow into the wells wasabout 2-3 seconds with respect to the test results illustrated above.

The oxide/PEG-coated micro-plates were prepared as follows: The surfaceof the polystyrene plate was exposed to an oxygen plasma (150 sccm q atan RF power of about 200 W in an Applied MicroStructures' MVD™ processchamber) for 5 minutes in order to clean the surface and create hydroxylavailability on the polystyrene surface. SiCl₄ was charged to theprocess chamber from a SiCl₄ vapor reservoir, where the SiCl₄ vaporpressure in the vapor reservoir was 18 Torr, creating a partial pressureof 2.4 Torr in the coating process chamber. Within 5 seconds, a firstvolume of H₂O vapor was charged to the process chamber from a H₂O vaporreservoir, where the H₂O vapor pressure in the vapor reservoir was 18Torr. A total of five chamber volumes of H₂O were charged, creating apartial pressure of 6.0 Torr in the coating process chamber. The totalpressure in the coating process chamber was 9 Torr. The substratetemperature and the temperature of the process chamber walls was about35° C. The substrate was exposed for a time period of about 10 minutesafter each H₂O addition. The silicon oxide coating thickness obtainedwas about 150 Å.

To apply the mPEG coating, mPEG (methoxy(polyethyleneoxy)propyltrimethoxysilane, Gelest P/N SIM 6492.7, MW=450-620, or methoxy(polyethyleneoxy)propyltrichlorosilane, Gelest P/N SIM 6492.66,MW=450-620) was charged to the process chamber from an mPEG vaporreservoir, where the mPEG vapor pressure in the vapor reservoir wasabout 2 Torr. Four chamber volumes of mPEG were charged, creating apartial pressure of 650 mTorr in the coating process chamber. Thesubstrate was exposed to mPEG vapor each time for a time period of 15minutes. The substrate temperature and the temperature of the processchamber walls was about 350° C. The mPEG coating thickness obtained wasabout 20 Å.

The HTS micro-plate embodiment illustrates the use of a hydrophiliccoating to draw a water-based substance into wells in an HTS micro-platewhich is formed from plastic In one embodiment, the interior of thewells has been coated to provide a hydrophilic surface, while theexterior surface of the plate remains hydrophobic because it has notbeen coated. This may be accomplished using a masking material over theplastic surface exterior of the wells during application of a coatingwhich provides a hydrophilic surface over the interior of the wells. Thehydrophobic surface surrounding a well helps force the water-baseddroplet into the hydrophilic interior of the well, and reduces thepossibility of well-to-well contamination of samples being tested.

EXAMPLE TEN

As discussed in the Background Art herein, poly(dimethylsiloxane),commonly known as PDMS, is frequently used in the fabrication ofmicrofluidics devices and in fabrication of Bio MEMS. Bio-compatibility,low costs and ease of PDMS substrate fabrication makes this materialattractive for both research and commercial applications. However, dueto the naturally strong hydrophobic surface properties of PDMS, it isdifficult to use this material in an application where fluid flowthrough microfluidic channels is required, as voids or bubbles tend toform within the channels.

We tried several different techniques for the treatment of a PDMSsubstrate surface, to produce a longer-lasting more hydrophilic surface.We prepared a PDMS substrate by casting a flat sheet from Sylgard-184precursor supplied by Dow Corning. The basic polymeric componentincluded dimethyl siloxane; dimethylvinyl-terminated, dimethylvinylated,and tirmethylated silica; and tetra(trimethylsiloxy) silane. The curingagent included dimethyl, methylhydrogen siloxane; dimethyl siloxane;dimethylvinyl-terminated, dimethylvinylated, and trimethylated silica;and tetramethyl tetravinyl cyclotetrasiloxane. The ratio of basicpolymeric component to curing agent used was 10:1. The mixture of basicpolymeric component with curing agent was poured over a glass slide andallowed to stand for 1 hour. The mixture was then cured at 65° C. forfour hours in an ambient air furnace. The thickness of the curedsubstrate sheet was about one mm. As illustrated in FIG. 12A, the waterdroplet contact angle on the surface of the cured PDMS sheet was about125 °.

With reference to FIG. 12B, for purposes of comparison, a the PDMSsubstrate surface was treated with a remotely-generated oxygen plasma,of the kind previously discussed herein with reference to applicants'apparatus for a time period of about five minutes. This converted thePDMS surface to a more desirable hydrophilic state, but this state wasshort lived, as the rearrangement of atoms occurs rapidly, bringinghydrophobic groups to the surface of the substrate. As illustrated incurve 1226 of graph 1220 in FIG. 12B, the water droplet contact angle ofthe PDMS surface immediately after the oxygen plasma treatment haddropped from the initial contact angle of about 120° to a contact angleof about 6°. However, after a time period of one day in ambient air atroom temperature (about 25° C.), the water droplet contact angle of onthe PDMS substrate surface had increased to about 64°. After four days,the contact angle had increased to about 90°.

With reference to FIG. 12A, treatment of the PDMS substrate surface byUV radiation in combination with ozone (in this instance created by theUV ionization of the oxygen in air), followed by treatment with aremotely-generated plasma, provided an improvement in the lifetime ofthe hydrophilic surface created on the PDMS substrate surface. The ozoneconcentration which was obtained from the U.V. radiation in air was inthe range of about 1%. The use of higher ozone concentrations, up toabout 5%, for example, and not by way of limitation, will significantlyshorten the length of treatment time required to take the water dropletcontact angle of the PDMS surface to its base level of about 6°, so thatthe treatment time will be a few minutes, and more commerciallyacceptable for production.

The PDMS surface treatment using a UV radiation source was carried outat a temperature of about 25° C. under atmospheric for a time period upto 60 minutes, in the presence of stagnant air. The wavelength of the UVradiation was in a range from 172 nm to 254 nm, depending on theradiation source used, and the UV flux density in the process chamberranged from about 20 mW/cm² to about 0.2 W/cm². It is anticipated thatUV flux density up to about 1.0 W/cm² would be useful, that thetreatment temperature may range from about 20° C. to about 80° C., andthat the pressure at which treatment is carried out may range from about1 Torr to about atmospheric pressure. Subatmospheric treatment of thePDMS surface in a process chamber in which a vapor deposition coatingmay be applied over the PDMS surface, i.e. “in-situ” PDMS surfacetreatment, is contemplated as advantageous. In less than 10 minutesafter completion of the ozone/UV treatment, the PDMS substrate wastreated with the remotely-generated oxygen plasma in the mannerpreviously described herein, for a five minute time period.

FIG. 12A shows a graph 1200 of the water droplet contact angle for agiven PDMS substrate surface in degrees on axis 1204, as a function ofthe amount of ozone/UV treatment time in minutes on axis 1202. Theoxygen plasma treatment time was constant for each PDMS-treated sampleat five minutes. Change in the contact angle for each substrate was alsomeasured as the substrate aged in air at atmospheric pressure and roomtemperature. The Change in contact angle for each substrate due to theozone/UV treatment is shown as a function of the time in minutes thesample was ozone/UV treated (excluding the oxygen plasma treatment) onaxis 1202. The change in contact angle due to aging is shown by Curves1206, 1208, 1210, 1212, 1214, 1216, and 1218. Curve 1206 shows the “astreated” sample prior to any aging. Curve 1208 shows the change incontact angle for each substrate after an aging time period of one day.Curve 1210 shows the change after two days of aging, Curve 1212 showsthe change after days, Curve 1214 shows the change after 6 days, Curve1216 shows the change after 7 days, and Curve 1218 shows the changeafter 14 days.

The data shows that ozone/UV treatment for a time period of about 35minutes or more under the conditions specified above provides theminimal achievable contact angle for the PDMS surface. There is somepermanent effect produced by the treatment ozone/UV treatment, as aminor reduction in contact angle from about 123° to about 100° remainseffective out to 14 days. However, for contact angles lower than about100°, where the ozone/UV treatment time period is sufficiently long toproduce a more drastic effect in hydrophilicity of the substratesurface, to contact angle as low as about 6°, the contact angle returnsto about 75° after 14 days of aging, no matter how long the ozone/UVtreatment time period. For example, a PDMS surface treated for 35minutes or more, to reduce the contact angle to about 6° shows a contactangle increases to about 38° to 43° after one day, with an increase from6° to about 75° after 14 days.

A PEG layer was deposited over the ozone/UV/oxygen plasma treatedsubstrate in the manner previously described herein with respect toExample Nine. The PEG applied was of a molecular weight range of about400 to 600. The coating precursor used was the chlorosilane type, withno other functional groups attached. A methoxy silane or an ethoxysilane may be used as well. A monolayer thickness of the PEG wasapplied. As illustrated by Curve 1230 on graph 1220 of FIG. 12B, thelifetime of the PEG-comprising hydrophilic surface produced was animprovement over the treated PDMS surface without a PEG deposition. Thewater droplet contact angle after 14 days of ambient air aging was 63°.

As can be seen from FIG. 12B, the use of an ozone/UV/oxygen plasmasurface treatment of a PDMS substrate provides a significant improvementin the lifetime of a hydrophilic surface formed on the substrate, whencompared with an oxygen plasma-treated PDMS surface. The depositionreactive PEG precursor over the ozone/UV/oxygen plasma treated surfaceprovides an even greater improvement, extending the number of days aftersubstrate preparation during which the substrate surface retained ahydrophilic nature, compared with the ozone/UV/oxygen plasma treatedsurface absent PEG. However, we have concluded that we had not depositeda PEG layer over the entire surface of the substrate, since a coating ofthe entire surface should provide a surface upon which the contact angledoes not change with time. A comparison of Curves 1228 and 1230 on graph1220 (FIG. 12 B) shows that there is a relatively constant difference incontact angle between the PDMS substrate which was ozone/UV/oxygenplasma treated (Curve 1228) and the PDMS substrate which was furthermodified by depositing of a PEG precursor on the surface (Curve 1230).This constant difference is attributed to the presence of the PEG on aportion of the substrate surface, while the continual change in thecontact angle itself is attributed to a continual change in thehydrophilicity of the portion of the substrate to which the PEGprecursor did not attach.

While the embodiment examples described in Example Ten were forsubstrates where the base polymeric material used as a precursor was adimethyl siloxane, other silicones (siloxanes) may be treated in asimilar manner to reduce the hydrophobic nature of the silicone surface.Further, as improved PEG coverage of a treated substrate is achieved,the overall change in water contact angle on the surface of the siloxanesubstrate after aging is expected to be further reduced.

As discussed above with respect to other substrate materials such assilicon, glass, stainless steel, polystyrene, and acrylic, a siloxanesubstrate my be coated with functional organic layers and used inBioMEMS. The functional layers may be other than the PEG layer discussedabove. We have observed that an ozone/UV-treated surface present on asiloxane will provide improved surface coverage and stability for anattached functional layer which bonds with a hydrophilic surface.

The above described exemplary embodiments are not intended to limit thescope of the present invention, as one skilled in the art can, in viewof the present disclosure expand such embodiments to correspond with thesubject matter of the invention claimed below.

1. A method converting a surface of a siloxane substrate from ahydrophobic nature, where a water droplet contact angle is in a range ofabout 90 degrees to about 130 degrees, to a hydrophilic nature, wheresaid water droplet contact angle ranges from about 5 degrees to about 50degrees, wherein said surface of said siloxane substrate is treated withozone in the presence of UV radiation, wherein a biocompatiblevapor-deposited coating is applied over said siloxane substrate treatedwith ozone in the presence of UV radiation, and where said biocompatiblecoating includes at least one organic functional layer, wherein saidmethod comprises the steps of: a) exposing said surface of said siloxanesubstrate to an ozone-comprising gas in a processing chamber, wherein UVradiation is applied during exposure of said siloxane surface to saidozone-comprising gas; b) subsequently, without exposure of said ozoneand UV radiation treated siloxane substrate to ambient conditions whichcontaminate or react with said treated surface, exposing said surface toa silicon chloride containing vapor in the presence of moisture, to forma hydrophilic silicon oxide layer on said treated siloxane substratesurface; and c) subsequently, without exposure of said hydrophilicsilicon oxide layer to ambient conditions which contaminate or reactwith said hydrophilic silicon oxide layer, exposing said silicon oxidelayer to a functionalized silane precursor vapor to form a layerselected from the group consisting of a monolayer, a self-alignedmonolayer, and a polymerized cross-linked layer.
 2. A method inaccordance with claim 1, wherein said UV radiation exhibits a wavelengthranging from about 172 nm to about 254 nm, and a UV flux density rangingfrom about 20 mW/cm² to about 1.0 W/cm².
 3. A method in accordance withclaim 2, wherein said UV flux density ranges from about 50 mW/cm² toabout 0.2 W/cm².
 4. A method in accordance with claim 2, wherein thetreatment time period of said siloxane surface with a combination ofozone and UV radiation ranges from about 60 minutes to about 1 minute.5. A method in accordance with claim 4, wherein said treatment iscarried out at a temperature ranging from about 20° C. to about 80° C.6. A method in accordance with claim 2, wherein said treatment iscarried out at a pressure ranging from about 1 Torr to about atmosphericpressure.
 7. A method in accordance with claim 1, wherein said siloxaneis PDMS.
 8. A method in accordance with claim 1 or claim 2, wherein saidsiloxane substrate is treated with ozone in the presence of UVradiation, followed by deposition of a PEG layer.
 9. A method inaccordance with claim 1 or claim 2, wherein said siloxane substrate istreated with ozone in the presence of UV radiation, followed by anoxygen plasma, followed by deposition of a PEG layer.
 10. A method inaccordance with claim 1 or claim 2, wherein a layer of PEG is appliedover said siloxane substrate, where said siloxane substrate has beentreated with a plasma which includes ozone in the presence of UVradiation.
 11. A method in accordance with claim 10, wherein said plasmawhich includes ozone also includes oxygen.
 12. A method in accordancewith claim 8, wherein said layer of PEG is applied using a vapordeposition technique which includes a stagnation reaction step.
 13. Amethod in accordance with claim 9, wherein said layer of PEG is appliedusing a vapor deposition technique which includes a stagnation reactionstep.
 14. A method in accordance with claim 10, wherein said layer ofPEG is applied using a vapor deposition technique which includes astagnation reaction step.
 15. A method in accordance with claim 11,wherein said layer of PEG is applied using a vapor deposition techniquewhich includes a stagnation reaction step.
 16. A method in accordancewith claim 1 or claim 2 wherein said biocompatible coating includes atleast one oxide-based layer and at least one organic functional layer.17. A method in accordance with claim 1, wherein said at least oneorganic functional layer includes a surface layer which is generatedfrom a polyethylene glycol-comprising precursor.
 18. A method inaccordance with claim 16, wherein said at least one organic functionallayer includes a surface layer which is generated from a polyethyleneglycol-comprising precursor.
 19. A method in accordance with claim 1,including an additional step: d) repeating steps a) through c), orrepeating steps b) through c), or repeating step c) a nominal number oftimes, without exposing said substrate to ambient conditions.
 20. Amethod in accordance with claim 19, wherein said processing chamberpressure subatmospheric pressure during step a) ranges from about 1 Torrto about 1 atmosphere.
 21. A method in accordance with claim 1, whereinsaid silicon chloride-containing precursor in step b) is silicontetrachloride.